mmdemux: dont set pkt->size to an invalid value.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 0c97fd336e17535239ab44d755a0d957dc2688f3)
1 file changed