s4:dsdb/paged_results: fix segfault in paged_results()

s4:dsdb/paged_results: fix segfault in paged_results()

It can happen that the paged_results() failes, e.g. due to
LDB_ERR_TIME_LIMIT_EXCEEDED, if that happens we should not
dereference ares->response, if ares is NULL.

We also should not call ldb_module_done() if paged_results()
fails, as it was already called.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14952

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>