avcodec/hevc_ps: Check return code from pps_range_extensions()

Fixes out of array read
Fixes: asan_heap-oob_177e222_885_cov_1532528832_MERGE_D_TI_3.bit
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>