avcodec/hevc: fix nb_sh / nb_sps check

fixes integer overflow

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/hevc: check slice_header_extension data length

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/hevc_ps: more complete check for vps_max_dec_pic_buffering

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/hevc_ps: Check layer_id_included_flags count

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>