multimedia/vapoursynth: Update to R64

Backport upstream commits:
8c68f4d42349aa3ba87ec3700a12e7fb38867748
31979d78dbe49c081b7da3ca1f7949433d83ca24
ad8bee27e37789ab01b82538e26db72d4128208d

Changelog: https://github.com/vapoursynth/vapoursynth/releases/tag/R64

References:
https://github.com/vapoursynth/vapoursynth/commit/8c68f4d42349aa3ba87ec3700a12e7fb38867748
https://github.com/vapoursynth/vapoursynth/commit/31979d78dbe49c081b7da3ca1f7949433d83ca24
https://github.com/vapoursynth/vapoursynth/commit/ad8bee27e37789ab01b82538e26db72d4128208d