Add option to fade in/out volume change

src/advanced-scene-switcher.cpp

@@ -444,6 +444,13 @@ void SwitcherData::Stop()
 	server.stop();
 	client.disconnect();
 
+	for (auto &t : audioHelperThreads) {
+		if (t.joinable()) {
+			t.join();
+		}
+	}
+	audioHelperThreads.clear();
+
 	if (showSystemTrayNotifications) {
 		DisplayTrayMessage(
 			obs_module_text("AdvSceneSwitcher.pluginName"),