libcli/security: check again for NULL values

libcli/security: check again for NULL values

BUG: https://bugzilla.samba.org/show_bug.cgi?id=156067

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Mon Mar 18 02:51:08 UTC 2024 on atb-devel-224

(cherry picked from commit b815abe77991d7929717ea3ed4b9d7bef7179715)

Autobuild-User(v4-20-test): Jule Anger <janger@samba.org>
Autobuild-Date(v4-20-test): Wed Mar 20 12:03:45 UTC 2024 on atb-devel-224