CVE-2022-42898 source4/heimdal: PAC parse integer overflows

CVE-2022-42898 source4/heimdal: PAC parse integer overflows

Catch overflows that result from adding PAC_INFO_BUFFER_SIZE.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15203

Heavily edited by committer Nico Williams <nico@twosigma.com>, original by
Joseph Sutton <josephsutton@catalyst.net.nz>.

Signed-off-by: Nico Williams <nico@twosigma.com>
[jsutton@samba.org Zero-initialised header_size in krb5_pac_parse() to
 avoid a maybe-uninitialized error; added a missing check for ret == 0]

[jsutton@samba.org Backported to our older version of Heimdal; removed
 lib/krb5/test_pac.c which we don't have]