Some old DV AVI files have the DSF-Flag of frames set to 0, although it
is PAL (maybe rendered with an old Ulead Media Studio Pro) ... this causes
ffmpeg/VLC-player to produce/play corrupted video (other players/editors
like VirtualDub work fine).

Fixes ticket #8333 and replaces/extends hack for ticket #2177
Signed-off-by: Marton Balint <cus@passwd.hu>