nss: refuse previously loaded certificate from file

... when we are not asked to use a certificate from file
static void display_cert_info(struct Curl_easy *data,
                              CERTCertificate *cert)
{
  char *subject, *issuer, *common_name;
  PRExplodedTime printableTime;
  char timeString[256];
  PRTime notBefore, notAfter;

  subject = CERT_NameToAscii(&cert->subject);
  issuer = CERT_NameToAscii(&cert->issuer);
  common_name = CERT_GetCommonName(&cert->subject);
  infof(data, "\tsubject: %s\n", subject);

  CERT_GetCertTimes(cert, &notBefore, &notAfter);
  PR_ExplodeTime(notBefore, PR_GMTParameters, &printableTime);
  PR_FormatTime(timeString, 256, "%b %d %H:%M:%S %Y GMT", &printableTime);
  infof(data, "\tstart date: %s\n", timeString);
  PR_ExplodeTime(notAfter, PR_GMTParameters, &printableTime);
  PR_FormatTime(timeString, 256, "%b %d %H:%M:%S %Y GMT", &printableTime);
  infof(data, "\texpire date: %s\n", timeString);
  infof(data, "\tcommon name: %s\n", common_name);
  infof(data, "\tissuer: %s\n", issuer);

  PR_Free(subject);
  PR_Free(issuer);
  PR_Free(common_name);
}

static void display_cert_info(struct Curl_easy *data,
                              CERTCertificate *cert)
{
  char *subject, *issuer, *common_name;
  PRExplodedTime printableTime;
  char timeString[256];
  PRTime notBefore, notAfter;

  subject = CERT_NameToAscii(&cert->subject);
  issuer = CERT_NameToAscii(&cert->issuer);
  common_name = CERT_GetCommonName(&cert->subject);
  infof(data, "\tsubject: %s\n", subject);

  CERT_GetCertTimes(cert, &notBefore, &notAfter);
  PR_ExplodeTime(notBefore, PR_GMTParameters, &printableTime);
  PR_FormatTime(timeString, 256, "%b %d %H:%M:%S %Y GMT", &printableTime);
  infof(data, "\tstart date: %s\n", timeString);
  PR_ExplodeTime(notAfter, PR_GMTParameters, &printableTime);
  PR_FormatTime(timeString, 256, "%b %d %H:%M:%S %Y GMT", &printableTime);
  infof(data, "\texpire date: %s\n", timeString);
  infof(data, "\tcommon name: %s\n", common_name);
  infof(data, "\tissuer: %s\n", issuer);

  PR_Free(subject);
  PR_Free(issuer);
  PR_Free(common_name);
}
