framework/av: Fix to handle corrupted .m4a clips

- Some m4a clips with corrupted header causes native crash
  in mediaserver.
- This is due to a wrong sample size which had to read from the clip.
- Fixed this by checking for the sample size extracted from the clip
  against the mediabuffer size.

Change-Id: If19b4bb2b99fb5558ed78d55d4e53fd03f6f8c73