Clear the steps from Player 1 when deleting them in ScreenEditMenu.

src/ScreenEditMenu.cpp

@@ -81,6 +81,7 @@ void ScreenEditMenu::HandleScreenMessage( const ScreenMessage SM )
 
 		Song* pSong = GAMESTATE->m_pCurSong;
 		Steps* pStepsToDelete = GAMESTATE->m_pCurSteps[PLAYER_1];
+		GAMESTATE->m_pCurSteps[PLAYER_1].Set(NULL);
 		bool bSaveSong = !pStepsToDelete->WasLoadedFromProfile();
 		pSong->DeleteSteps( pStepsToDelete );
 		SONGMAN->Invalidate( pSong );