lib: handle NTTIME_THAW in nt_time_to_full_timespec()

lib: handle NTTIME_THAW in nt_time_to_full_timespec()

Preliminary handling of NTTIME_THAW to avoid NTTIME_THAW is passed as some
mangled value down to the VFS set timestamps function.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14127
RN: Avoid storing NTTIME_THAW (-2) as value on disk

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
(cherry picked from commit 6ed71ad7e6aa98a34cfde95d7d62c46694d58469)

Autobuild-User(v4-14-test): Jule Anger <janger@samba.org>
Autobuild-Date(v4-14-test): Wed Nov 10 15:54:35 UTC 2021 on sn-devel-184