If you scroll and draw to the left of the origin, when you export the scene, there's a weird whitespace on the right. This is because we do the min() computation starting at 0 and not -Infinity This also fixes pasted elements and scrollbars.
* normalize dimensions of non-linear elements * fix element type check regression
Fixes #490. Preserves the ratio of the preview image when width / height reaches max-width/max-height
