output-layout: improve closest point for no outputs case

Without outputs, all points are equally invalid anyway, but for e.g.
cursor warping it makes more sense to preserve the original position.

include/wlr/types/wlr_output_layout.h

@@ -120,6 +120,7 @@ bool wlr_output_layout_intersects(struct wlr_output_layout *layout,
 /**
  * Get the closest point on this layout from the given point from the reference
  * output. If reference is NULL, gets the closest point from the entire layout.
+ * If the layout is empty, the result is the given point itself.
  */
 void wlr_output_layout_closest_point(struct wlr_output_layout *layout,
 	struct wlr_output *reference, double lx, double ly,

types/wlr_output_layout.c

@@ -302,7 +302,7 @@ void wlr_output_layout_closest_point(struct wlr_output_layout *layout,
 		return;
 	}
 
-	double min_x = 0, min_y = 0, min_distance = DBL_MAX;
+	double min_x = lx, min_y = ly, min_distance = DBL_MAX;
 	struct wlr_output_layout_output *l_output;
 	wl_list_for_each(l_output, &layout->outputs, link) {
 		if (reference != NULL && reference != l_output->output) {