libstagefright: Use channel count if channel mask is zero.

-If the channel mask which is part of the meta data is zero use
 a valid channel count to update the channel mask.
-PCM offload playback for wav clips fails for some clips because
 channel mask part of the wave header is zero.

CRs-Fixed: 664374
Change-Id: I1bd5f2cc56fbc1eb9a6e04d219185690d3ce409c
libstagefright: Fix app crash during pcm offload playback

 -ANR is seen with trick mode operations during
  pcm offload playback.
 -If Player issues the read request to omx client while omx client is
  in pausing state, it moves the client to executing state if variable
  mPasued is true and it never returns from pause.
 -Do not set the variable mPaused to true while it is in pausing state.

Change-Id: Ib824f3a651f738be26df8906d7175eb59ce82fab