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