avcodec/hevc_ps: Check delta_pocs in ff_hevc_decode_short_term_rps()

Fixes: integer overflow
Fixes: 2893/clusterfuzz-testcase-minimized-5809330567774208

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
