avcodec/hevcdec: Check luma/chroma_log2_weight_denom

Fixes: signed integer overflow: 3 + 2147483647 cannot be represented in type 'int'
Fixes: 5888/clusterfuzz-testcase-minimized-5634701067812864

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg


Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>