Get the formdata stored in the database for existing slice.
        params: slice_id: integer

def query_form_data(self):
        """
        Get the formdata stored in the database for existing slice.
        params: slice_id: integer
        """
        form_data = {}
        slice_id = request.args.get('slice_id')
        if slice_id:
            slc = db.session.query(models.Slice).filter_by(id=slice_id).one_or_none()
            if slc:
                form_data = slc.form_data.copy()

        update_time_range(form_data)

        return json.dumps(form_data)