ctdb-common: Fix use-after-free error in comm_fd_handler()

ctdb-common: Fix use-after-free error in comm_fd_handler()

BUG: https://bugzilla.samba.org/show_bug.cgi?id=12580

comm_write_send() creates a new tevent_req and adds it to the queue
of requests to be processed.  If this tevent_req is freed, then the
queue entry is not removed causing use-after-free error.

If the tevent_req returned by comm_write_send() is freed, then that
request should be removed from the queue and any pending actions based
on that request should also be removed.

Signed-off-by: Amitay Isaacs <amitay@gmail.com>
Reviewed-by: Martin Schwenke <martin@meltin.net>