harden h264 decoding to prevent some crashes when input data is corrupted.

Patch by Frank %eucloid A gmail P com%
date: Jan 18, 2007 6:48 PM
subject: Re: [Ffmpeg-devel] h264, protection against corrupted data (second try patch)
AND
date: Jan 17, 2007 8:22 PM
subject: [Ffmpeg-devel] h264, protection against corrupted data

this also fixes a possible security issue (the sps and pps ids where not checked,
then used as index into an array of sps/pps structs which was then filled with data from the bitstream)

Originally committed as revision 7585 to svn://svn.ffmpeg.org/ffmpeg/trunk