Fixes out of array read
Fixes: 7fcd09eadd046e326d8ea0af66f166c8/asan_heap-oob_4a52e5_2273_fa6078a10dd575df266fb1e0b4114cd5.avi

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>