Avoid OOB reads in nal parsing.

BUG=112670
Review URL: https://chromiumcodereview.appspot.com/9340008

git-svn-id: http://src.chromium.org/svn/trunk/deps/third_party/ffmpeg/source@120671 4ff67af0-8c30-449e-8e8b-ad334ec8d88c
1 file changed