[1.7.x] Fixed #22720 -- Migrations attempt to create _order twice.

        if self.order_with_respect_to:

            self.order_with_respect_to = self.get_field(self.order_with_respect_to)

            self.ordering = ('_order',)

            if not any(isinstance(field, OrderWrt) for field in model._meta.local_fields):

                model.add_to_class('_order', OrderWrt())

        else:

            self.order_with_respect_to = None