lib: Enable watching and storing dbwrap_watch records.

lib: Enable watching and storing dbwrap_watch records.

Samba so far on a dbwrap_watch record either watches or stores a
record, but never both from the same db_record instance acquired from
a dbwrap_fetch_locked(). In one of the next commits this will change,
we will watch a record and at the same time store data into it. This
patch enables a watch_send() followed by a storev() by properly
keeping the watchers around.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>