After processing several X events, X11DRV_MsgWaitForMultipleObjects always
tells us that a new message is available. This is not true for some cases.

For instance, when we call DestroyWindow, the X queues DestroyEvent. Then,
X11DRV_MsgWaitForMultipleObjects handles the event only; none is posted or
sent as hwnd for destroyed window is unavailable. However, the function
states "new message is available" by returning count - 1 value.

This is an issue for CoWaitForMultipleHandles because it expects a new
message in the queue and consumes the message.
Signed-off-by: Akihiro Sagawa <sagawa.aki@gmail.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>