CVE-2019-12098: krb5: always confirm PA-PKINIT-KX for anon PKINIT

RFC8062 Section 7 requires verification of the PA-PKINIT-KX key excahnge
when anonymous PKINIT is used.  Failure to do so can permit an active
attacker to become a man-in-the-middle.

Introduced by a1ef548600c5bb51cf52a9a9ea12676506ede19f.  First tagged
release Heimdal 1.4.0.

CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N (4.8)

Change-Id: I6cc1c0c24985936468af08693839ac6c3edda133
Signed-off-by: Jeffrey Altman <jaltman@auristor.com>
Approved-by: Jeffrey Altman <jaltman@auritor.com>
(cherry picked from commit 38c797e1ae9b9c8f99ae4aa2e73957679031fd2b)
find_pa_data(const METHOD_DATA *md, unsigned type)
{
    size_t i;
    if (md == NULL)
	return NULL;
    for (i = 0; i < md->len; i++)
	if (md->val[i].padata_type == type)
	    return &md->val[i];
    return NULL;
}

find_pa_data(const METHOD_DATA *md, unsigned type)
{
    size_t i;
    if (md == NULL)
	return NULL;
    for (i = 0; i < md->len; i++)
	if (md->val[i].padata_type == type)
	    return &md->val[i];
    return NULL;
}
