passdb: spare superfluous call to lookup_rids() in lookup_sids()

passdb: spare superfluous call to lookup_rids() in lookup_sids()

If we have no name indexes for a domain, all names were domain
names and have been resolved earlier, including the domain name.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=10463

Change-Id: I5a7a387fa89d2b2bdd465c13b3dca0e18ca0482c
Signed-off-by: Michael Adam <obnox@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Autobuild-User(master): Stefan Metzmacher <metze@samba.org>
Autobuild-Date(master): Tue Feb 25 11:17:18 CET 2014 on sn-devel-104