Project created in 20.12.1c project renders different number of frames in 22.08.1

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

To reproduce:

1. Open effects-stylize-20.12.1.kdenlive from erjiang/kdenlive-backcompat
2. Render out the project in both versions listed above
3. See that the render output of 20.12.1c has 300 frames and the render output of 22.08.1 has 301 frames.