[qsoundeffect] Play samples only when resources are available.
[qaudiooutput] Close output before destroying resource policy.
[resourcepolicy-plugin] Check for isDestroyed() in destructor.
[qgstreamerplayercontrol] Add resource release timer when pausing or stopping media.

If media is paused, stopped, or end of media, if state hasn't changed to
playing state, release the resources. The idea with the timer is that if
for example media player is playing one song which ends, there won't be
release()/acquire() unnecessarily if next song is immediately set as
media and started playing.
[qaudiooutput] Improvements to resource handling.
[qsoundeffect] Check initial availability for resources.
[qaudiooutput] Add release timer for resources.