If something quickly maps and unmaps a window, then we'll immediately
create and destroy the Wayland surface that cooresponds to that
window. If our mouse pointer is over the window when the surface is
created, we'll receive a enter on the window.
Since resource creation and destruction is not synchronous, that
means that the compositor will queue up an event for a resource that's
eventually destroyed. On the client-side, when we receive this message,
we note that the resource isn't allocated, and get a NULL surface in our
enter handler. We immediately try to dereference this, and then crash.
This was caused by running gtkperf while moving the window a lot.
Reviewed-by: Daniel Stone <daniel@fooishbar.org>
Signed-off-by: Jasper St. Pierre <jstpierre@mecheye.net>
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