avcodec/hevc_ps: More complete window reset

Fixes out of array read
Fixes: signal_sigsegv_35bcf26_471_cov_2806540268_CAINIT_A_SHARP_4.bit
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
