doublesound fix

src/audio/AudioEventHandler.cpp

@@ -29,6 +29,7 @@ namespace gdw {
 				break;
 			case Event::TRAKTORBEAM_REVERSE_ACTIVATED:
 			case Event::TRAKTORBEAM_ACTIVATED:
+				this->engine.audio().stop_sound(this->channels["beam"]);
 				this->channels["beam"] = this->engine.audio().queue_sound("tractorBeam", -1);
 				this->engine.audio().sound_volume(60, this->channels["beam"]);
 				break;