winbind: Fix a memleak

winbind: Fix a memleak

Bug: https://bugzilla.samba.org/show_bug.cgi?id=14388
Signed-off-by: Laurent Menase <laurent.menase@hpe.com>
Reviewed-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Noel Power <noel.power@suse.com>
Autobuild-User(master): Volker Lendecke <vl@samba.org>
Autobuild-Date(master): Mon Sep 14 13:33:13 UTC 2020 on sn-devel-184

(cherry picked from commit 8f868b0ea0b4795668f7bc0b028cd85686b249fb)

Autobuild-User(v4-11-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-11-test): Mon Oct  5 11:17:23 UTC 2020 on sn-devel-184