Fix motion blur

[wahn]

I'm working on an issue about motion blur on the Blender side and noticed that the test scene works for C++, but not for the Rust implementation:

This is how it is supposed to look like. The responsible lines in the scene description are:

...
TransformTimes 0.0 1.0 
WorldBegin
...
    ActiveTransform EndTime
    Rotate -45 0 0 1
    ActiveTransform All
...
WorldEnd

[wahn]

Commit ba63f60 fixes the problem.