Fix crash on exit

src/quickvnc/qvncitem.cpp

@@ -101,9 +101,10 @@ void QVncItem::geometryChange(const QRectF &newGeometry, const QRectF &oldGeomet
 bool QVncItem::eventFilter(QObject *, QEvent *event)
 {
     if (event->type() == QEvent::CursorChange) {
-        qDebug() << "Cursor change!" << window()->cursor();
-        if (m_vncServer) {
-            auto newCursor = window()->cursor();
+        QWindow *w = window();
+        if (w && m_vncServer) {
+            //qDebug() << "Cursor change!" << w->cursor();
+            auto newCursor = w->cursor();
             m_vncServer->setCursor(&newCursor);
         }
     }