source3/passdb: Fix NULL dereference in _lsa_LookupSids()

source3/passdb: Fix NULL dereference in _lsa_LookupSids()

When lookup_sids() returns NT_STATUS_NONE_MAPPED but exits early without
populating the names array, the subsequent dereference of names causes a
NULL pointer dereference.

Return an appropriate error status that allows existing error handling
to catch this case before the NULL dereference occurs.

Signed-off-by: Anoop C S <anoopcs@samba.org>
Reviewed-by: Martin Schwenke <martin@meltin.net>