Fixes: 39a25908b84604acdaa490138282d091_signal_sigsegv_7ffff713351a_331_WAWV.avi with memlimit of 262144

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