Fix SongManager::Invalidate. Call it from places it is needed:

ScreenEdit::RevertFromDisk, ScreenEdit's Save routine, and
ScreenEditMenu's Delete Steps routine.  This fixes the bug where
deleting a step chart sometimes causes interesting behavior
but usually just causes a CTD next time you run Oni mode.  It also makes
sure data precalculated from the songs is correctly recalculated when
ScreenEdit changes a song.

stepmania/src/ScreenEditMenu.cpp

@@ -74,6 +74,7 @@ void ScreenEditMenu::HandleScreenMessage( const ScreenMessage SM )
 		Steps* pStepsToDelete = GAMESTATE->m_pCurSteps[PLAYER_1];
 		bool bSaveSong = !pStepsToDelete->WasLoadedFromProfile();
 		pSong->DeleteSteps( pStepsToDelete );
+		SONGMAN->Invalidate( pSong );
 
 		/* Only save to the main .SM file if the steps we're deleting were loaded
 		 * from it. */