Gradfun produces bright-green highlights (regression between 20.12.1c and 22.08.1)

To reproduce:

1. Open effects-grain-and-noise-20.12.1.kdenlive from erjiang/kdenlive-backcompat
2. Render out the project in both versions listed above
3. See that the version rendered by 22.08.1 has some highlights blown out as black or bright green, while the version rendered by 20.12.1c does not.

Tested with kdenlive-20.12.1c-x86_64.appimage, kdenlive-22.08.1-x86_x64.AppImage on Ubuntu 22.04.