add asserts

stepmania/src/ScreenEdit.cpp

@@ -489,6 +489,9 @@ REGISTER_SCREEN_CLASS( ScreenEdit );
 ScreenEdit::ScreenEdit( CString sName ) : Screen( sName )
 {
 	LOG->Trace( "ScreenEdit::ScreenEdit()" );
+
+	ASSERT( GAMESTATE->m_pCurSong );
+	ASSERT( GAMESTATE->m_pCurSteps[0] );
 }
 
 void ScreenEdit::Init()