fix LockInputSecs not being set correctly, and pressing Start early would choose without starting SM_GoToNextScreen

stepmania/src/ScreenSelect.cpp

@@ -183,8 +183,8 @@ void ScreenSelect::HandleScreenMessage( const ScreenMessage SM )
 
 		SCREENMAN->RefreshCreditsMessages();
 
-		if( !IsTransitioning() )
-			StartTransitioningScreen( SM_GoToNextScreen );
+		ASSERT( !IsTransitioning() );
+		StartTransitioningScreen( SM_GoToNextScreen );
 	}
 
 	ScreenWithMenuElements::HandleScreenMessage( SM );

stepmania/src/ScreenSelectMaster.cpp

@@ -269,9 +269,10 @@ void ScreenSelectMaster::BeginScreen()
 
 	this->UpdateSelectableChoices();
 
-	m_fLockInputSecs = this->GetTweenTimeLeft();
-
 	ScreenSelect::BeginScreen();
+
+	// Call GetTweenTimeLeft after the base BeginScreen has started the in Transition.
+	m_fLockInputSecs = this->GetTweenTimeLeft();
 }
 
 void ScreenSelectMaster::HandleScreenMessage( const ScreenMessage SM )