The big NULL replacement party part 2.

This may take a bit. Trying to do this by operator/command.

src/ScreenDemonstration.cpp

@@ -57,7 +57,7 @@ void ScreenDemonstration::Init()
 
 	ScreenJukebox::Init();
 
-	if( GAMESTATE->m_pCurSong == NULL )	// we didn't find a song.
+	if( GAMESTATE->m_pCurSong == nullptr )	// we didn't find a song.
 	{
 		PostScreenMessage( SM_GoToNextScreen, 0 );	// Abort demonstration.
 		return;