Keep aspect ratio only work when pressing CTRL before moving handle

[DamirPorobic]

I tried SHIFT because CTRL did not seem to work. Much later, I realized that I had to depress CTRL before beginning to resize, and that it had no effect when pressed while dragging. I guess that is also a bit non-standard, since usually one can press CTRL while dragging to preserve the aspect ratio while resizing.

Originally posted by @pascal-niklaus in ksnip/ksnip#610 (comment)

[DamirPorobic]

Fixed