Merge changes from topic "backport-cpu-usage-bugs" into qt-qpr1-dev

* changes:
  MPEG4Extractor: check the default sample info before checking the validity of sample size.
  Add size checking for 'saiz' box
  Add more size checking for 'stts' box
  Add more size checking for 'stss' box
  Add size checking for 'saio' box