Today, async_set_completion_callback() is used to register a function
that is called when the async I/O is completed.  It is assumed that the
async will eventually be queued when such callback is registered.

However, this incurs extra complexity in future code that needs the
completion logic to be invoked even if the async is never actually
queued (e.g. when the I/O failed synchronously before async_handoff).

Generalise async completion callback by calling it in async_handoff()
when the I/O status indicates failure.
Signed-off-by: Jinoh Kang <jinoh.kang.kr@gmail.com>
Signed-off-by: Zebediah Figura <zfigura@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>