scene: use scene_node_get_size in wlr_scene_node_at

This allows to unify the RECT and BUFFER code-paths. The BUFFER one
will become more complicated with destination size and transforms.

types/scene/wlr_scene.c

@@ -528,14 +528,11 @@ struct wlr_scene_node *wlr_scene_node_at(struct wlr_scene_node *node,
 		struct wlr_scene_surface *scene_surface = wlr_scene_surface_from_node(node);
 		intersects = wlr_surface_point_accepts_input(scene_surface->surface, lx, ly);
 		break;
-	case WLR_SCENE_NODE_RECT:;
-		struct wlr_scene_rect *rect = scene_rect_from_node(node);
-		intersects = lx >= 0 && lx < rect->width && ly >= 0 && ly < rect->height;
-		break;
+	case WLR_SCENE_NODE_RECT:
 	case WLR_SCENE_NODE_BUFFER:;
-		struct wlr_scene_buffer *scene_buffer = scene_buffer_from_node(node);
-		intersects = lx >= 0 && lx < scene_buffer->buffer->width &&
-			ly >= 0 && ly < scene_buffer->buffer->height;
+		int width, height;
+		scene_node_get_size(node, &width, &height);
+		intersects = lx >= 0 && lx < width && ly >= 0 && ly < height;
 		break;
 	}