return early if selmon is not part of the output layout in dirtomon()

instead of checking twice

dwl.c

@@ -1168,12 +1168,12 @@ Monitor *
 dirtomon(enum wlr_direction dir)
 {
 	struct wlr_output *next;
-	if (wlr_output_layout_get(output_layout, selmon->wlr_output)
-			&& (next = wlr_output_layout_adjacent_output(output_layout,
+	if (!wlr_output_layout_get(output_layout, selmon->wlr_output))
+		return selmon;
+	if ((next = wlr_output_layout_adjacent_output(output_layout,
 			dir, selmon->wlr_output, selmon->m.x, selmon->m.y)))
 		return next->data;
-	if (wlr_output_layout_get(output_layout, selmon->wlr_output)
-			&& (next = wlr_output_layout_farthest_output(output_layout,
+	if ((next = wlr_output_layout_farthest_output(output_layout,
 			dir ^ (WLR_DIRECTION_LEFT|WLR_DIRECTION_RIGHT),
 			selmon->wlr_output, selmon->m.x, selmon->m.y)))
 		return next->data;