Fewer calls to RingBuffer::Put in case of trailing zeroes...

... so there is only one update per track of the atomics in RingBuffer in each
pass of the loop in FillBuffers, which will be needed to synchronize RingBuffer
and TimeQueue correctly.

src/AudioIO.h

@@ -778,8 +778,6 @@ private:
    bool                mInputMixerWorks;
    float               mMixerOutputVol;
 
-   GrowableSampleBuffer mSilentBuf;
-
    AudioIOListener*    mListener;
 
    friend class AudioThread;