client: Abort when trying to add an event to a destroyed queue

Detect when we are trying to add an event to a destroyed queue,
and abort instead of causing a use-after-free memory error.

This situation can occur when an wl_event_queue is destroyed before
its attached wl_proxy objects.

Signed-off-by: Alexandros Frantzis <alexandros.frantzis@collabora.com>
13 jobs for !282 with warn-wl-event-queue-use-after-free in 2 minutes and 55 seconds (queued for 35 seconds)
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