Merge remote-tracking branch 'qatar/release/0.5' into release/0.5

* qatar/release/0.5:
  Fix memory (re)allocation in matroskadec.c, related to MSVR-11-0080.
  cavs: fix some crashes with invalid bitstreams
  mjpeg: Detect overreads in mjpeg_decode_scan() and error out.

Merged-by: Michael Niedermayer <michaelni@gmx.at>