FlacEncoder: handle EOS properly.

 - If EOS comes with first frame, notifyFillBuffer for outbuffer was not done.
 - When EOS comes after last frame, it was setting timestamp to 0,
   consider timestamp from valid frames only.

Test: testSimpleEncodeNative[8(audio/flac)]
Test: testOnlyEos[8(audio/flac)]
Test: testOnlyEosNative[8(audio/flac)]
Test: testSimpleEncode[8(audio/flac)]
Bug: 156203931

Change-Id: I9510bc284c5318aa6d1832993490fbcffb6d2151
1 file changed