Prevent divide by zero in WAVExtractor

In the case that mNumChannels, bytesPerSample, or mSampleRate are
zero, a divide by zero occurs. None of these parameters of a WAV
file should ever be zero. Check that they aren't and return an error
otherwise.

Bug: 23285883

Change-Id: Id67b8620944405ca59572221f6f1c2b19c363e69