Remove unnecessary isValid() check on segments without intersections.
Remove unnecessary isValid() check on segments without intersections.

It was only causing issues without solving anything.

lehni/paper.js,iconexperience/paper.js,byte-foundry/paper.js,byte-foundry/paper.js,iconexperience/paper.js,iconexperience/paper.js,lehni/paper.js,lehni/paper.js,byte-foundry/paper.js