Build fix for older ffmpeg.
Build fix for older ffmpeg.

svn path=/trunk/libavg/; revision=8892

hoodie/libavg,scotty007/libavg,libavg/libavg,yyd01245/libavg,yyd01245/libavg,yyd01245/libavg,yyd01245/libavg,hoodie/libavg,scotty007/libavg,libavg/libavg,th3infinity/libavg,libavg/libavg,hoodie/libavg,scotty007/libavg,th3infinity/libavg,th3infinity/libavg,scotty007/libavg,libavg/libavg,th3infinity/libavg,hoodie/libavg