Timeline preview render doesn't take into account composite and transform effect.

STEPS TO REPRODUCE

1. 1-add a video track to the timeline
2. 2-add a png image with alpha channel on top of it
3. 3-add composite and transform effect
4. 4-prerender the timeline

OBSERVED RESULT

The rendered view in the project monitor lacks the composited image on top of the original video. It only works when the timeline preview render profile is set to MJPEG but that also strangely cuts the monitor fps in half. All the other profiles don't work as aspected

EXPECTED RESULT

The timeline prerender should correctly composite all the tracks.

KDE Neon Kdenlive 19.04.2 from the official repositories