Fix A/V (de)sync with discontinuous NSV streams,

Patch by Joakim elupus A ecce P se
Original thread:
Subject: [Ffmpeg-devel] [PATCH]: A/V sync on nsv streams.
Date: October 27, 2006 3:18:54 AM CEDT
Actual committed patch:
Date: October 28, 2006 3:23:28 AM CEDT

Originally committed as revision 6826 to svn://svn.ffmpeg.org/ffmpeg/trunk