This fixes issue1907
Patch by Thomas Devanneaux gmail(thomdev)
backport r23078 by benoit
Originally committed as revision 23211 to svn://svn.ffmpeg.org/ffmpeg/branches/0.6
contains NAL units previous to the IDR where the SPS/PPS was inserted.
Ok:ed by Benoit on irc.
Originally committed as revision 11482 to svn://svn.ffmpeg.org/ffmpeg/trunk