Merge pull request #255 from sigatrev/SyncMachine

fix ScreenGameplaySyncMachine crash
dear github: our travis build is broken in a pretty serious way (The command "sudo apt-get install libc6-dev" failed and exited with 100), and I know this isn't travis-support nor the right place for it but I thought I should let someone outside of IRC know the reason for it thanks

src/ScreenGameplaySyncMachine.cpp

@@ -94,6 +94,10 @@ void ScreenGameplaySyncMachine::HandleScreenMessage( const ScreenMessage SM )
 
 	if( SM == SM_GoToPrevScreen || SM == SM_GoToNextScreen )
 	{
+		FOREACH_PlayerNumber( pn )
+		{
+			GAMESTATE->m_pCurSteps[pn].Set( NULL );
+		}
 		GAMESTATE->m_PlayMode.Set( PlayMode_Invalid );
 		GAMESTATE->SetCurrentStyle( NULL );
 		GAMESTATE->m_pCurSong.Set( NULL );