dix: avoid calling deleted block and wakeup handlers

dix: avoid calling deleted block and wakeup handlers

BlockHandler and WakeupHandlers may be removed within a different
BlockHandler or WakeupHandler, especially since config/udev uses
these and removes devices.

Calling the deleted handlers and passing potentially freed data
can result in the X server segfaulting after device removal, or
events that result in device removal such as undocking or suspend/
resume.

Signed-off-by: Scott James Remnant <scott@netsplit.com>
Reviewed-by: Daniel Stone <daniel@fooishbar.org>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>