playsink: fix audio passthrough hang when set play rate

when audio passthrough is enable, audio_filter will not been put into audiochain. When do reconfigure, playsink will remove previous audio chain as audio_filter is not match with chain->filter (should be NULL). Then playsink will remove audio chain and recreate. When remove, streamsynchroinizer will release its sinkpad, but sinkpad is in waiting all pad eos as audio is eos in fast forward 4X mode and hold stream lock, release pad will also try to lock this stream lock and cause hang. Need check whether chain->filter is valided first to avoid recreate audio chain