[HEVC] unable to handle IDR_W_RADL

if a hevc clip has a IDR_W_RADL type nal, and has a RADL_N before that IDR (negative POC), mkvmerge is not able to generate a correct timestamp. (note that it seems fine with v55, but not ok after v56)

sample file (around 5.547s): https://6.gigafile.nu/0420-c943ef677fdb727c67307410912d51881