XCB: update the platformwindows version of Qt::WindowState

when the event comes from the windowing system

Task-number: QTBUG-31117

Change-Id: Id136ad8c39c9284cbd6ad126ee71ac655f8f91ef
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

src/plugins/platforms/xcb/qxcbwindow.cpp

@@ -1859,6 +1859,7 @@ void QXcbWindow::handlePropertyNotifyEvent(const xcb_property_notify_event_t *ev
         if (m_lastWindowStateEvent != newState) {
             QWindowSystemInterface::handleWindowStateChanged(window(), newState);
             m_lastWindowStateEvent = newState;
+            m_windowState = newState;
         }
         return;
     }