Fixes pixel format selection
Fixes out of array accesses
Fixes: asan_heap-oob_1766029_6_asan_heap-oob_20aa045_332_cov_1823216757_m2-d1d366d7965db766c19a66c7a2ccbb6b.tif

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>