xwm: fix a crash in handle_state

To produce the bug, build and run: (you don't need the game data to test)

https://github.com/clintbellanger/flare-engine/

$ mv ~/.config/flare ~/.config/flare.bak
$ ./flare  # click 'configure', set full screen mode then click 'ok'
           # weston will crash and dump core.

[Pekka: edited the commit message]
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
1 file changed