b474325aa1
Caused by ab43c57a2a
The VSE allows for "no scene", prior to above commit an "arbitrary"
framerate of 25 was hardcoded to display "something" in that case.
To resolve, pick what we defined as default for framerate (getting rid
of the "arbitrary") in case we have no (VSE) scene.
NOTE: that is 24 atm (instead of the hardcoded 25 we had before)
Pull Request: https://projects.blender.org/blender/blender/pulls/146300