[Cin] ChomaKey's old bug

[Andrea paz]

In an exchange of mails Igor Vladimirsky pointed out to me that the
old bug reported by Camille:

https://lists.cinelerra-gg.org/pipermail/cin/2021-March/003149.html
and:
https://www.cinelerra-gg.org/bugtracker/view.php?id=559

Has been fixed by Adam in CinHV. The patch with the fix is at:

https://github.com/heroineworshiper/hvirtual/commit/9080ca3fc952edce68fcabb6d7460dda7c75da79

Andrew, do you think it is possible to implement the patch in CinGG?