cursor: ignore wlr_cursor_set_surface() with same surface

Avoids damaging the output and rendering the cursor again if it
hasn't changed.

types/wlr_cursor.c

@@ -462,6 +462,10 @@ void wlr_cursor_set_surface(struct wlr_cursor *cur, struct wlr_surface *surface,
 
 	struct wlr_cursor_output_cursor *output_cursor;
 	wl_list_for_each(output_cursor, &cur->state->output_cursors, link) {
+		if (surface == output_cursor->surface) {
+			continue;
+		}
+
 		cursor_output_cursor_reset_image(output_cursor);
 
 		output_cursor->surface = surface;