avcodec/alsdec: check predictor order against block length

Fixes out of array access
Fixes: abd3c041acbcb816be113455d138166b-asan_heap-oob_b11634_3707_cov_1707137151_als_05_2ch48k16b.mp4
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
