This fixes a bug where sometimes self.box.aspect_ratio would be a negati...

This fixes a bug where sometimes self.box.aspect_ratio would be a negative number, which throws an error when you try and set scale by getting the square root of a negative number.

I'm not 100% sure why scale is set this way to begin with or if `self.box.aspect_ratio` being negative is a problem in and of itself, hence the pull request.