multimedia/vapoursynth: update to R53

Changes: http://www.vapoursynth.com/2021/04/r53-once-more-there-are-bug-fixes/
Changes: https://github.com/vapoursynth/vapoursynth/compare/R52...R53
Reported by: GitHub (watch releases)

(cherry picked from commit 8b7214f15623cfef66fd30d8d7a7539e44de24e5)