LXVST: dispatch close when GUI is destroyed

see also e635571f2f

gtk2_ardour/linux_vst_gui_support.cc

@@ -782,6 +782,7 @@ vstfx_launch_editor (VSTState* vstfx)
 void
 vstfx_destroy_editor (VSTState* vstfx)
 {
+	assert (!gui_quit);
 	pthread_mutex_lock (&vstfx->lock);
 	if (vstfx->linux_window) {
 		vstfx->destroy = TRUE;

gtk2_ardour/lxvst_plugin_ui.cc

@@ -42,6 +42,7 @@ LXVSTPluginUI::LXVSTPluginUI (boost::shared_ptr<PlugInsertBase> pib, boost::shar
 LXVSTPluginUI::~LXVSTPluginUI ()
 {
 	_resize_connection.disconnect();
+	vstfx_destroy_editor (_vst->state ());
 
 	// plugin destructor destroys the custom GUI, via the vstfx engine,
 	// and then our PluginUIWindow does the rest