Fixes use of uninitialized memory
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 007498fc1a639ecee2cda1892cbcff66c7c8c951)
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>