mtk/rectangle: Add constructor for an empty rectangle

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3703>

mtk/mtk/mtk-rectangle.c

@@ -65,6 +65,12 @@ mtk_rectangle_new (int x,
   return rect;
 }
 
+MtkRectangle *
+mtk_rectangle_new_empty (void)
+{
+  return g_new0 (MtkRectangle, 1);
+}
+
 /**
  * mtk_rectangle_area:
  * @rect: A rectangle

mtk/mtk/mtk-rectangle.h

@@ -86,6 +86,9 @@ MtkRectangle * mtk_rectangle_new (int x,
                                   int width,
                                   int height);
 
+MTK_EXPORT
+MtkRectangle * mtk_rectangle_new_empty (void);
+
 /* Basic comparison functions */
 MTK_EXPORT
 int mtk_rectangle_area (const MtkRectangle *rect);