Fix frei0r producer not working with tractor.
Fix frei0r producer not working with tractor.

Reported in https://forum.shotcut.org/t/color-bars-working-not-
correctly/8308

j-b-m/mlt,mltframework/mlt,mltframework/mlt,j-b-m/mlt,j-b-m/mlt,mltframework/mlt,j-b-m/mlt,mltframework/mlt,j-b-m/mlt,j-b-m/mlt,mltframework/mlt,j-b-m/mlt,mltframework/mlt,j-b-m/mlt,mltframework/mlt,mltframework/mlt,mltframework/mlt,j-b-m/mlt,j-b-m/mlt,mltframework/mlt