signal potential fullscreen change to the menaubar directly..

..instead of using the signal

src/mixxx.cpp

@@ -529,7 +529,7 @@ void MixxxMainWindow::initialize(QApplication* pApp, const CmdlineArgs& args) {
     // Connect signals to the menubar. Should be done before emit newSkinLoaded.
     connectMenuBar();
     // Refresh the Fullscreen checkbox for the case we went fullscreen earlier
-    emit fullScreenChanged(isFullScreen());
+    m_pMenuBar->onFullScreenStateChange(isFullScreen());
 
     launchProgress(63);