Handle Sound.play returning null, and free the SOUND_COMPLETE listener.
Handle Sound.play returning null, and free the SOUND_COMPLETE listener.

Fixes #188, fixes #182.

playedonline/flambe,markknol/flambe,mikedotalmond/flambe,Disar/flambe,mikedotalmond/flambe,Disar/flambe,Disar/flambe,weilitao/flambe,aduros/flambe,mikedotalmond/flambe,weilitao/flambe,aduros/flambe,weilitao/flambe,markknol/flambe,mikedotalmond/flambe,aduros/flambe,playedonline/flambe,weilitao/flambe,Disar/flambe,playedonline/flambe,playedonline/flambe,markknol/flambe,aduros/flambe