reenable sound in Cancel(), rather than as a special case in the input, so it works if someone else calls Cancel

stepmania/src/ScreenDemonstration.cpp

@@ -87,6 +87,12 @@ void ScreenDemonstration::HandleScreenMessage( const ScreenMessage SM )
 	ScreenJukebox::HandleScreenMessage( SM );
 }
 
+void ScreenDemonstration::Cancel( ScreenMessage smSendWhenDone )
+{
+	ScreenAttract::SetAttractVolume( false ); // unmute attract sounds
+	ScreenJukebox::Cancel( smSendWhenDone );
+}
+
 /*
  * (c) 2003-2004 Chris Danford
  * All rights reserved.

stepmania/src/ScreenDemonstration.h

@@ -11,6 +11,7 @@ class ScreenDemonstration : public ScreenJukebox
 public:
 	ScreenDemonstration();
 	virtual void Init();
+	virtual void Cancel( ScreenMessage smSendWhenDone );
 
 	virtual void HandleScreenMessage( const ScreenMessage SM );