Update to upstream release 56.1.0.
Details:
- Enhancements and fixes, see https://mkvtoolnix.download/doc/NEWS.md
- In particular, fix a regression in the HEVC parser causing invalid memory access.
MFH: 2021Q2
(cherry picked from commit 2a0f957e621567aa84ff55748d3f59781af43d90)