add seed number to seed point.

[SamTov]

If a seed point is given, no seed number is computed leading to an error.

def _seed_process(self, visualize: bool):
        """
        Seed an RND process.

        Parameters
        ----------
        visualize : bool
                if true, visualization is performed on the data. This parameter is
                populated by the build_dataset method.

        Returns
        -------
        Initializes an RND process.
        """
        if self.seed_point:
            seed_point = self.seed_point
        else:
            # seed_point = self.fetch_data(1)
            seed_number = onp.random.randint(0, len(self.generator))
            seed_point = self.generator.take_index(seed_number)

        self._update_target_set(np.array(seed_point))
        self._retrain_network()
        self.target_indices.append(seed_number)
        if visualize:
            self.update_visualization(reference=False)