Stop use after free

Fixes bug #10087

Thanks to Man Min Yan for their analysis and providing a solution to the issue.

Reviewed-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>

Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Fri Sep 27 14:29:46 CEST 2013 on sn-devel-104
(cherry picked from commit 6bf9a774718917c3429fa1492f5b0268ae5e01c3)

Autobuild-User(v4-1-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-1-test): Wed Feb  5 13:12:49 CET 2014 on sn-devel-104
s3-winbind: Improve performance of wb_fill_pwent_sid2uid_done().

BUG: https://bugzilla.samba.org/show_bug.cgi?id=2191

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>

Autobuild-User(master): Andreas Schneider <asn@cryptomilk.org>
Autobuild-Date(master): Thu Jan 16 20:17:24 CET 2014 on sn-devel-104

(cherry picked from commit 1a43778433934530d77791edd1af538de8b1d8a3)
Signed-off-by: Andreas Schneider <asn@samba.org>

Autobuild-User(v4-1-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-1-test): Thu Feb  6 13:59:54 CET 2014 on sn-devel-104