Determine the next insert offset according to storage.

        Returns:
            int: The next insert offset.

def nextindx(self):
        '''
        Determine the next insert offset according to storage.

        Returns:
            int: The next insert offset.
        '''
        indx = 0
        with s_lmdbslab.Scan(self.slab, self.db) as curs:
            last_key = curs.last_key()
            if last_key is not None:
                indx = s_common.int64un(last_key) + 1
        return indx