xwm: Don't try to read deleted properties

src/xwayland/window-manager.c

@@ -646,6 +646,9 @@ weston_wm_handle_property_notify(struct weston_wm *wm, xcb_generic_event_t *even
 
 	fprintf(stderr, "XCB_PROPERTY_NOTIFY: window %d, ",
 		property_notify->window);
+	if (property_notify->state == XCB_PROPERTY_DELETE)
+		fprintf(stderr, "deleted\n");
+	else
 		read_and_dump_property(wm, property_notify->window,
 				       property_notify->atom);