krb5: bump to version 1.13.3 and fix uninitialized warning/error

krb5: bump to version 1.13.3 and fix uninitialized warning/error

Version 1.13.3 has a tar.gz so the OpenWRT default Build/Prepare
rule can be used with MD5 checksum.

Add patch to fix build:
ktutil_funcs.c: In function 'ktutil_delete':
ktutil_funcs.c:75:28: error: 'prev' may be used uninitialized in this function [-Werror=maybe-uninitialized]
                 prev->next = lp->next;

There does not seem to be a way for 'prev' being uninitialized
(logically), however the compiler does not see that, because
'prev' is dependent on i >= 1.
So, we just need to initialize it to NULL.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>