classicupgrade: treat old never expires value right

classicupgrade: treat old never expires value right

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14624

Signed-off-by: Bjoern Jacke <bjacke@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Autobuild-User(master): Stefan Metzmacher <metze@samba.org>
Autobuild-Date(master): Wed Feb 10 15:06:49 UTC 2021 on sn-devel-184

(cherry picked from commit df75d82c9de6977c466ee9f01886cb012a9c5fef)

Autobuild-User(v4-12-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-12-test): Tue Feb 16 22:33:52 UTC 2021 on sn-devel-184