Blender Git Loki

VSE: Fix video strip duration calculation

The video duration was not read correctly from the video file.

It would use the global duration of the file which does in some cases
not line up with the actual duration of the video stream.
Now we take the video stream duration and start time into account when
calculating the strip duration.

Reviewed By: Richard Antalik

Differential Revision: https://developer.blender.org/D11920