Change perspective dot's position bar limit depending of layer's size.

[AkaneAngele]

So, you create a dot. The dot's position bar lets you move the dot to a maximum of 100 pixels X or Y. You can surpass this limit writing the position or using the mouse wheel.

So, what if the limit is the layer's size. I dunno how much trouble it can do, but there's the idea.

[OverloadedOrama]

Implemented by fba01c1