libtasn1: Fix the potential buffer overrun

libtasn1: Fix the potential buffer overrun

In _asn1_tag_der(), the first while loop for the long form may end up
with a "k" value with "ASN1_MAX_TAG_SIZE" and cause the buffer overrun
in the second while loop. This commit tweaks the conditional check to
avoid producing a too large "k".

This is a quick fix and may differ from the official upstream fix.

libtasn1 issue: https://gitlab.com/gnutls/libtasn1/-/issues/49

Signed-off-by: Gary Lin <glin@suse.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Tested-by: Stefan Berger <stefanb@linux.ibm.com>