menu view: position widgets initially at (0, 0)

The default 'Rect' constructor constructs an invalid rectangle where the
p1 coordinates are lower than the p2 coordinates. In particular, p1 is
set to (1, 1). The 'Widget' implementation uses the points individually
as input into the 'Animated_rect' mechanism. This way, widgets end up
being positioned at (1, 1) initially and are moved to (0, 0) once the
first layout update is applied. By explicitly initializing the
'_geometry' to (0x0+0+0), we avoid this initial artifact.

repos/gems/src/app/menu_view/widget.h

@@ -155,7 +155,7 @@ class Menu_view::Widget : List_model<Widget>::Element
 		 * Position relative to the parent widget and actual size, defined by
 		 * the parent
 		 */
-		Rect _geometry { };
+		Rect _geometry { Point(0, 0), Area(0, 0) };
 
 		Animated_rect _animated_geometry { _factory.animator };