This old code can cause 'hwiu' problem

[sprhawk]

commit: c9cbb7b

If quickly change songs with different audio streamer instances, it may cause 'hwiu' problem.

Because When quickly change/skip songs , program first 'stop's current audiostreamer instance, then creates a new instance.　But during quick changin, the first instance may be during 'WAITING_FOR_DATA' state, and - (void)stop just returned, and the instance is released. However the old thread start a new audio queue then, the new instance cannot re-start a AQ, returned a 'hwiu'