Fix potential PAC processing crash

An input to krb5_pac_parse() with a zero-length buffer at the end of
the PAC can cause an assertion failure in k5_pac_locate_buffer() due
to an off-by-one error.  Correct the assertion.

[ghudson@mit.edu: edited commit message]

(cherry picked from commit 331e393c6def46c00b6b54e1b2a0d1080c2af9e0)

https://github.com/krb5/krb5/commit/79b244de8be6902a4af2c78e6619a815a1df8722
Author: Arjun <pkillarjun@protonmail.com>
Committer: Greg Hudson <ghudson@mit.edu>
Commit: 79b244de8be6902a4af2c78e6619a815a1df8722
Branch: krb5-1.21
 src/lib/krb5/krb/pac.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)