* adding code to skip over JUNK. It turns out that video editing
     software uses junk to resize ix## chunks without actually
     scrubbing the data. That trips up our packet extraction
     code since it recognizes ix## entries as "packets". Basically
     we have to skip over JUNK chunks for exactly the same reason
     we have to skip over ix## entries.

Originally committed as revision 3378 to svn://svn.ffmpeg.org/ffmpeg/trunk