Resize a window.
Redimensionne une fenêtre.
_window_ : ObjGtk : any window already created.
_width_ : I : the new width. If _width_ is nil or < 1, _width_ will be set to 1. If a minimal size has been defined, _width_ can't be smaller than it.
_height_ : I : the new height. If _height_ is nil or < 1, _height_ will be set to 1. If a minimal size has been defined, _height_ can't be smaller than it.
Return : ObjGtk : the same window or nil if error.