This is validated by tests introduced in
59beffb4 etc. This commit alone doesn't fix said
tests, because:

* on this poll, we will alert the waiting async;

* when reselecting, we will still request POLLIN, because the AFD_POLL_READ
  request is still active,

* when POLLIN is subsequently signaled, we do not remove it in
  sock_dispatch_asyncs(), because we check async_waiting(), not async_queued().
Signed-off-by: Zebediah Figura <zfigura@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>