Fixes out of array read
Fixes: asan_heap-oob_35ca682_1474_cov_3230122439_aletrek_tga_16bit.mov
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 1895d414aaacece3b57d7bf19502305e9a064fae)
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>