nuplayer: Don't write data to sink if sink is stopped

 Capture images with camera in quick succession
 then after few iterations shutter sound stops coming.

 In good case, once the EOS is encountered by NuPlayerRenderer,
 it stops AudioSink and send notification to NuPlayer with
 some delay. In turn NuPlayerDriver handles this EOS,
 by pausing NuPlayer. And then seek to 0 request comes for next
 shutter sound playback which gets handled correctly. But in bad
 case, when NuPlayerRenderer send EOS notification with some delay
 to NuPlayer, before NuPlayer handles it, new seek request comes.
 So in this case the NuPlayerRenderer have stopped AudioSink,
 but NuPlayer/NuPlayerDriver is not aware of this, and keeps
 pumping data to NuPlayerRenderer. But as the AudioSink is stopped
 nothing gets rendered and by the time NuPlayerRenderer resume gets
 called in the start of  NuPlayer, numFramesAvailableToWrite
 becomes zero. So NuPlayerRenderer does not call sink write.
 This continues till user exits camera application and
 launches it again.

 To fix this make sure if sink is stopped do not write any data to
 sink

CRs-Fixed: 823436
Change-Id: I9ed8f205740b237d23d4bb72e7c99d8d7104f87c