avcodec/hevc: allocate entries unconditionally

Fixes out of array access
Fixes: 08664a2a7921ef48172f26495c7455be/asan_heap-oob_23036c6_3301_523388ef84285a0270caf67a43247b59.bit

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
