Normalizes a Rect.
A Rect is defined by the area covered by its size; this means that a Rect with origin in [ 0, 0 ] and a size of [ 10, 10 ] is equivalent to a Rect with origin in [ 10, 10 ] and a size of [ -10, -10 ].
This function is useful to ensure that a rectangle has positive width and height; it will modify the passed this and normalize its size.
| this |
a Rect |