demux: avi: fix master track selection with nonseekable
demux: avi: fix master track selection with nonseekable

(otherwise drops packets)

xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc