gencache: Avoid a duplicate call to string_term_tdb_data

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

Autobuild-User(master): Volker Lendecke <vl@samba.org>
Autobuild-Date(master): Mon Sep  9 17:02:28 CEST 2013 on sn-devel-104