fix release FFmpegExtractor

old: release FFmpegExtractor -> release AV Tracks
now: release AV Tracks -> release FFmpegExtractor

Change-Id: I1fb60a78deb1c2a1cc4f23dff1786337ea24c684
add support for unknown formats.

The FFmpegExtractor support all ffmpeg formats!!!
Unknown format is defined as MEDIA_MIMETYPE_CONTAINER_FFMPEG

Change-Id: I1645591a1c53f5f2d961a0212e351533630b9999
Fix crash when playing ALAC

 * Don't crash when seeing a weird EOS packet.

Change-Id: I29e979ab94daccb9e81264e09f258c10d96373f5