ctdb-daemon: Schedule running of callback if there are no event scripts

ctdb-daemon: Schedule running of callback if there are no event scripts

The callback should never be called before an immediate return.  The
callback might reply to a control and the caller of
ctdb_event_script_callback_v() may not have assigned/stolen the
pointer to control structure into the private data.  Therefore,
calling the callback can dereference an uninitialised pointer to the
control structure when attempting to reply.

ctdb_event_script_callback_v() must succeed when there are no event
scripts.  On success the caller will mark the call as asynchronous and
expect the callback to be called.  Given that it can't be called
before return then it needs to be scheduled.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=12180

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>
(cherry picked from commit 9076c44f35bf309b9e183bae98829f7154b93f33)