UI: Fix audio filter changes not being added to undo

When a change to an audio filter was done, it would create a timer and
wait for no more inputs before saving and adding to undo (this is to
prevent spam from sliders). For some reason, the timer would get
destroyed before the information is saved, preventing it from going on
the undo stack.

UI/properties-view.hpp

@@ -59,6 +59,7 @@ public:
 	{
 		if (update_timer) {
 			update_timer->stop();
+			QMetaObject::invokeMethod(update_timer, "timeout");
 			update_timer->deleteLater();
 			obs_data_release(old_settings_cache);
 		}