Given a fully-qualified subdomain and a sequence number, get its historic subdomain record at that sequence.
        Raises SubdomainNotFound if there is no such subdomain

def get_subdomain_entry_at_zonefile_index(self, fqn, zonefile_index, cur=None):
        """
        Given a fully-qualified subdomain and a sequence number, get its historic subdomain record at that sequence.
        Raises SubdomainNotFound if there is no such subdomain
        """
        get_cmd = "SELECT * FROM {} WHERE fully_qualified_subdomain=? AND parent_zonefile_index=?".format(self.subdomain_table)
        cursor = None
        if cur is None:
            cursor = self.conn.cursor()
        else:
            cursor = cur

        db_query_execute(cursor, get_cmd, (fqn,zonefile_index))

        try:
            rowdata = cursor.fetchone()
            assert rowdata
        except Exception as e:
            raise SubdomainNotFound(fqn)

        return self._extract_subdomain(rowdata)