Ensure that the standalone plug-in saves its state when the OS sends a quit request

modules/juce_audio_plugin_client/Standalone/juce_StandaloneFilterApp.cpp

@@ -117,6 +117,9 @@ public:
     //==============================================================================
     void systemRequestedQuit() override
     {
+        if (mainWindow.get() != nullptr)
+            mainWindow->pluginHolder->savePluginState();
+
         if (ModalComponentManager::getInstance()->cancelAllModalComponents())
         {
             Timer::callAfterDelay (100, []()