Selections can be resized off-canvas

[Cameron White]

Steps to reproduce:

1) Rectangle Select, and draw some selection. Note that if you try to move the mouse outside the canvas, the selection is constrained to the edges.

2) Release the mouse, and then drag one of the corners to resize the selection. If you move the mouse off-canvas, the selection is not constrained as it was before.

[grofaty (grofaty)]

I can confirm this behavior. As I see after step 2 it is always constrained by two selection edges, but other two (opposite ones) are going off the canvas.

This is definitely not a regression. This is probably some ancient bug, because I have seen this for ages, never really thought it is a bug, so never reported it, because everything is working fine like e.g. "Crop to selection" from tools works fine.

The only draw back I currently see is a performance hit:
1. Create 16 x 16 image.
2. Zoom to 700.
3. Rectangle Selection and mark some small part of the image.
4. "Crop to selection" from toolbar.
5. (observe) Action is executed immediately.
6. Undo from toolbar.
7. Rectangle Selection. Release the mouse and move tho bottom-right corner and resize selection, but do it so that you will move the mouse very far (you know that your hand is stretched out as much as possible).
8. "Crop to selection" from toolbar.
9. (observe) Action is not executed immediately but instead takes some seconds. It probably depends on the speed of PC. My laptop is ancient one, so it is more noticeable. It looks internally program 'computes' and works on whole selection despite selection being off the canvas. This is not very ordinary sample to reproduce, so Low priority is perfectly fine.

[Cameron White (cameronwhite91)]

Fixed: https://github.com/PintaProject/Pinta/commit/629fea4b241fb698d97a5911c524a9728721826f