When adding sound strips, it would in some cases be offset
from the desired start position.
This was because some sound files had a start time that was not 0
even if they didn't have any video file associated with them.
Only try to shift the sound strip around if it is added with a video
strip.
Pull Request: https://projects.blender.org/blender/blender/pulls/127256
b4e5412a28