Sometimes the objects are not paginated. In this case we need to avoid trying to render pagination data, as it will throw an error. This guard clause also means we can remove messy conditionals from several controllers.
Extracts the JSON response from the admin's line item controller which
are only used by the bulk management feature into its own controller.
This decouples spree from an OFN-only feature and allows to remove
unnecessary code. Furthermore, Admin::LineItemsController is gone in
Spree 2.4.0.beta. See: https://github.com/spree/spree/pull/5280
