fix crash when decoding a truncated H264 slice

patch by Alexander Chemeris % ipse P ffmpeg A gmail.com %
Original thread:
date: Dec 5, 2006 7:26 PM
subject: [Ffmpeg-devel] [PATCH] Fix crush when truncated slice passed to H.264 decoder

Originally committed as revision 7229 to svn://svn.ffmpeg.org/ffmpeg/trunk