FIX Reindex fails if Versioned DataObject has no own table

If an DataObject extends an other DataObject without adding new dbfields, it will not have it's own table in the database. The sql query would break, since `$page->ClassName.ID` does not exist in the db.
Merge pull request #14 from johannesx75/patch-2

FIX Reindex fails if Versioned DataObject has no own table