dns: Always return SOA record for records we should know

dns: Always return SOA record for records we should know

Regression introduced by commit 4b54e14b7cf456e327b176b365e8471e0899210b,
where the number of returned records is not set by talloc_array_length
when the record is not found.

Found by DELL EMC at SDC SMB3 plugfest trying to perform a secure DNS
update.

Signed-off-by: Samuel Cabrero <scabrero@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
Autobuild-User(master): Samuel Cabrero <scabrero@samba.org>
Autobuild-Date(master): Fri Nov  8 12:31:30 UTC 2019 on sn-devel-184