Check stream type in AudioFlinger::createTrack

A bad parameter to AudioFlinger::createTrack could cause mediaserver to crash.

Other AudioFlinger stream type cleanup:
 - Simplify range check for audio_stream_type_t
 - Add comment about mStreamTypes array initialization.

Change-Id: Ia33aa1cce0fdd694b08d9288816ffc097a9543d0
3 files changed