Fixes out of array access
Fixes: signal_sigsegv_3670fc0_2818_cov_2307326154_moon.mux

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 79a98294)
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>