fix: fix customParseFormat plugin strict mode parse meridiem bug
fix #1238
Invalid dates are parsed resulting in incorrect values
e.g, 
const dt = dayjs('1993-51-11')
`dt.isValid()` returns `true` and `dt.format('YYYY-MM-DD')` returns `1997-03-11`
const dt = dayjs('1993-51-41')
`dt.isValid()` returns `true` and `dt.format('YYYY-MM-DD')` returns `1997-04-10`
infact `dayjs('1993-08-21', 'YYYY/MM/DD')` returns true for isValid()

isValid() should return false for all these 

**Information**
 - Day.js Version: v1.9.6
 - OS:  macOS 11 BigSur
 - Browser: chrome 86
 - Time zone: GMT

Invalid dates are parsed as valid
diff --git a/src/plugin/customParseFormat/index.js b/src/plugin/customParseFormat/index.js
index f2eabb2b7..12c7803e8 100644
--- a/src/plugin/customParseFormat/index.js
+++ b/src/plugin/customParseFormat/index.js
@@ -11,7 +11,7 @@ const matchSigned = /[+-]?\d+/ // -inf - inf
 const matchOffset = /[+-]\d\d:?(\d\d)?/ // +00:00 -00:00 +0000 or -0000 +00
 const matchWord = /\d*[^\s\d-:/()]+/ // Word
 
-let locale
+let locale = {}
 
 function offsetFromString(string) {
   if (!string) return 0
@@ -216,8 +216,9 @@ export default (o, C, d) => {
       const isStrict = isStrictWithoutLocale || isStrictWithLocale
       let pl = args[2]
       if (isStrictWithLocale) [,, pl] = args
-      if (!isStrictWithoutLocale) {
-        locale = pl ? d.Ls[pl] : this.$locale()
+      locale = this.$locale()
+      if (!isStrictWithoutLocale && pl) {
+        locale = d.Ls[pl]
       }
       this.$d = parseFormattedInput(date, format, utc)
       this.init()
@@ -226,7 +227,7 @@ export default (o, C, d) => {
         this.$d = new Date('')
       }
       // reset global locale to make parallel unit test
-      locale = undefined
+      locale = {}
     } else if (format instanceof Array) {
       const len = format.length
       for (let i = 1; i <= len; i += 1) {

diff --git a/test/plugin/customParseFormat.test.js b/test/plugin/customParseFormat.test.js
index ef8bfd625..bc78e74b8 100644
--- a/test/plugin/customParseFormat.test.js
+++ b/test/plugin/customParseFormat.test.js
@@ -294,6 +294,8 @@ describe('Strict mode', () => {
     const format = 'YYYY-MM-DD'
     expect(dayjs(input, format).isValid()).toBe(true)
     expect(dayjs(input, format, true).isValid()).toBe(false)
+    expect(dayjs('2020-Jan-01', 'YYYY-MMM-DD', true).isValid()).toBe(true)
+    expect(dayjs('30/1/2020 10:59 PM', 'D/M/YYYY h:mm A', true).isValid()).toBe(true)
   })
   it('with locale', () => {
     const input = '2018 三月 99'

{"test/plugin/customParseFormat.test.js": {"run": "PASS", "test": "FAIL", "fix": "PASS"}}
{"test/timezone.test.js:Add Time days (DST)": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/de.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/sk.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/advancedFormat.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/weekYear.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/timezone.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/isSameOrBefore.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/pluralGetSet.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/timezone.test.js:Diff (DST)": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/keys.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/utils.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/relativeTime.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/parse.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/localizedFormat.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/updateLocale.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/constructor.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/weekday.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/isLeapYear.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/query.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/localeData.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/timezone.test.js:UTC diff in DST": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/zh.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/ja.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/declarations.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/timezone.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/ru.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/dayOfYear.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/timezone.test.js:UTC add day in DST": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/manipulate.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/cs.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/en.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/get-set.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/he.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/utc.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/quarterOfYear.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/objectSupport.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/fi.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/sv.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/toArray.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/timezone.test.js:Utc Offset": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/utc-utcOffset.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/sr-cyrl.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/br.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/isMoment.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/isYesterday.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/pl.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/toObject.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/sr.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/preParsePostFormat.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/isSameOrAfter.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/weekOfYear.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/comparison.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/calendar.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/isTomorrow.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/et.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/hu.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/timezone.test.js:UTC and utcOffset": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/arraySupport.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/isToday.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/hr.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/badMutable.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/duration.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/isoWeek.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/minMax.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/isoWeeksInYear.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/uk.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/display.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/devHelper.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/buddhistEra.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/lt.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/zh-cn.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/locale/ar.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}, "test/plugin/isBetween.test.js": {"run": "PASS", "test": "PASS", "fix": "PASS"}}
{"test/plugin/customParseFormat.test.js": {"run": "PASS", "test": "FAIL", "fix": "PASS"}}
{"passed_count": 76, "failed_count": 0, "skipped_count": 0, "passed_tests": ["test/timezone.test.js:Add Time days (DST)", "test/get-set.test.js", "test/plugin.test.js", "test/locale/he.test.js", "test/locale/de.test.js", "test/plugin/utc.test.js", "test/locale/en.test.js", "test/plugin/quarterOfYear.test.js", "test/plugin/objectSupport.test.js", "test/locale/fi.test.js", "test/locale/sk.test.js", "test/locale/sv.test.js", "test/plugin/advancedFormat.test.js", "test/plugin/toArray.test.js", "test/plugin/weekYear.test.js", "test/timezone.test.js", "test/timezone.test.js:Utc Offset", "test/plugin/isSameOrBefore.test.js", "test/plugin/pluralGetSet.test.js", "test/timezone.test.js:Diff (DST)", "test/plugin/utc-utcOffset.test.js", "test/locale/sr-cyrl.test.js", "test/utils.test.js", "test/locale/br.test.js", "test/plugin/relativeTime.test.js", "test/parse.test.js", "test/locale/keys.test.js", "test/plugin/isMoment.test.js", "test/plugin/isYesterday.test.js", "test/locale/pl.test.js", "test/plugin/toObject.test.js", "test/locale/sr.test.js", "test/plugin/localizedFormat.test.js", "test/plugin/updateLocale.test.js", "test/constructor.test.js", "test/plugin/weekday.test.js", "test/plugin/preParsePostFormat.test.js", "test/plugin/isSameOrAfter.test.js", "test/plugin/weekOfYear.test.js", "test/comparison.test.js", "test/plugin/isLeapYear.test.js", "test/query.test.js", "test/plugin/localeData.test.js", "test/plugin/calendar.test.js", "test/plugin/isTomorrow.test.js", "test/locale/et.test.js", "test/timezone.test.js:UTC diff in DST", "test/locale/hu.test.js", "test/timezone.test.js:UTC and utcOffset", "test/plugin/arraySupport.test.js", "test/locale/zh.test.js", "test/plugin/isToday.test.js", "test/locale/ja.test.js", "test/plugin/declarations.test.js", "test/locale/hr.test.js", "test/plugin/timezone.test.js", "test/plugin/badMutable.test.js", "test/locale.test.js", "test/plugin/customParseFormat.test.js", "test/locale/ru.test.js", "test/plugin/duration.test.js", "test/plugin/isoWeek.test.js", "test/plugin/dayOfYear.test.js", "test/plugin/minMax.test.js", "test/plugin/isoWeeksInYear.test.js", "test/timezone.test.js:UTC add day in DST", "test/manipulate.test.js", "test/display.test.js", "test/plugin/devHelper.test.js", "test/locale/cs.test.js", "test/locale/uk.test.js", "test/locale/lt.test.js", "test/plugin/buddhistEra.test.js", "test/locale/zh-cn.test.js", "test/locale/ar.test.js", "test/plugin/isBetween.test.js"], "failed_tests": [], "skipped_tests": []}
{"passed_count": 75, "failed_count": 1, "skipped_count": 0, "passed_tests": ["test/timezone.test.js:Add Time days (DST)", "test/plugin.test.js", "test/get-set.test.js", "test/locale/de.test.js", "test/locale/he.test.js", "test/plugin/utc.test.js", "test/plugin/quarterOfYear.test.js", "test/plugin/objectSupport.test.js", "test/locale/fi.test.js", "test/locale/sk.test.js", "test/locale/ar.test.js", "test/locale/sv.test.js", "test/plugin/advancedFormat.test.js", "test/plugin/toArray.test.js", "test/plugin/weekYear.test.js", "test/timezone.test.js", "test/timezone.test.js:Utc Offset", "test/plugin/isSameOrBefore.test.js", "test/plugin/pluralGetSet.test.js", "test/timezone.test.js:Diff (DST)", "test/plugin/utc-utcOffset.test.js", "test/locale/sr-cyrl.test.js", "test/locale/br.test.js", "test/utils.test.js", "test/plugin/relativeTime.test.js", "test/parse.test.js", "test/locale/keys.test.js", "test/plugin/isMoment.test.js", "test/plugin/isYesterday.test.js", "test/locale/pl.test.js", "test/plugin/toObject.test.js", "test/locale/sr.test.js", "test/plugin/localizedFormat.test.js", "test/plugin/updateLocale.test.js", "test/constructor.test.js", "test/plugin/preParsePostFormat.test.js", "test/plugin/weekday.test.js", "test/plugin/isSameOrAfter.test.js", "test/plugin/weekOfYear.test.js", "test/plugin/isLeapYear.test.js", "test/comparison.test.js", "test/query.test.js", "test/plugin/localeData.test.js", "test/plugin/isTomorrow.test.js", "test/locale/et.test.js", "test/locale/hu.test.js", "test/timezone.test.js:UTC diff in DST", "test/plugin/calendar.test.js", "test/timezone.test.js:UTC and utcOffset", "test/plugin/arraySupport.test.js", "test/locale/zh.test.js", "test/plugin/isToday.test.js", "test/locale/ja.test.js", "test/plugin/declarations.test.js", "test/locale/hr.test.js", "test/plugin/timezone.test.js", "test/locale.test.js", "test/plugin/badMutable.test.js", "test/locale/ru.test.js", "test/plugin/duration.test.js", "test/plugin/isoWeek.test.js", "test/plugin/dayOfYear.test.js", "test/plugin/minMax.test.js", "test/plugin/isoWeeksInYear.test.js", "test/timezone.test.js:UTC add day in DST", "test/locale/uk.test.js", "test/display.test.js", "test/plugin/devHelper.test.js", "test/locale/cs.test.js", "test/plugin/buddhistEra.test.js", "test/locale/lt.test.js", "test/manipulate.test.js", "test/locale/zh-cn.test.js", "test/locale/en.test.js", "test/plugin/isBetween.test.js"], "failed_tests": ["test/plugin/customParseFormat.test.js"], "skipped_tests": []}
{"passed_count": 76, "failed_count": 0, "skipped_count": 0, "passed_tests": ["test/timezone.test.js:Add Time days (DST)", "test/get-set.test.js", "test/locale/he.test.js", "test/locale/de.test.js", "test/plugin.test.js", "test/locale/en.test.js", "test/plugin/utc.test.js", "test/plugin/quarterOfYear.test.js", "test/plugin/objectSupport.test.js", "test/locale/fi.test.js", "test/locale/sk.test.js", "test/locale/sv.test.js", "test/plugin/advancedFormat.test.js", "test/plugin/toArray.test.js", "test/plugin/weekYear.test.js", "test/timezone.test.js", "test/timezone.test.js:Utc Offset", "test/plugin/isSameOrBefore.test.js", "test/plugin/pluralGetSet.test.js", "test/timezone.test.js:Diff (DST)", "test/plugin/utc-utcOffset.test.js", "test/locale/sr-cyrl.test.js", "test/utils.test.js", "test/locale/br.test.js", "test/plugin/relativeTime.test.js", "test/parse.test.js", "test/locale/keys.test.js", "test/plugin/isMoment.test.js", "test/plugin/isYesterday.test.js", "test/locale/pl.test.js", "test/plugin/toObject.test.js", "test/locale/sr.test.js", "test/plugin/localizedFormat.test.js", "test/plugin/updateLocale.test.js", "test/constructor.test.js", "test/plugin/weekday.test.js", "test/plugin/isSameOrAfter.test.js", "test/plugin/preParsePostFormat.test.js", "test/plugin/weekOfYear.test.js", "test/comparison.test.js", "test/plugin/isLeapYear.test.js", "test/query.test.js", "test/plugin/localeData.test.js", "test/locale/et.test.js", "test/plugin/isTomorrow.test.js", "test/locale/hu.test.js", "test/timezone.test.js:UTC diff in DST", "test/plugin/calendar.test.js", "test/timezone.test.js:UTC and utcOffset", "test/plugin/arraySupport.test.js", "test/locale/zh.test.js", "test/plugin/isToday.test.js", "test/locale/ja.test.js", "test/plugin/declarations.test.js", "test/locale/hr.test.js", "test/plugin/timezone.test.js", "test/locale.test.js", "test/plugin/badMutable.test.js", "test/plugin/customParseFormat.test.js", "test/locale/ru.test.js", "test/plugin/duration.test.js", "test/plugin/isoWeek.test.js", "test/plugin/dayOfYear.test.js", "test/plugin/minMax.test.js", "test/plugin/isoWeeksInYear.test.js", "test/timezone.test.js:UTC add day in DST", "test/manipulate.test.js", "test/display.test.js", "test/plugin/devHelper.test.js", "test/locale/cs.test.js", "test/plugin/buddhistEra.test.js", "test/locale/lt.test.js", "test/locale/uk.test.js", "test/locale/zh-cn.test.js", "test/locale/ar.test.js", "test/plugin/isBetween.test.js"], "failed_tests": [], "skipped_tests": []}