Bug 22239: JavaScript error on subscription detail page when there are no orders

Bug 22239: JavaScript error on subscription detail page when there are no orders

This page modifies the subscription detail page so that a JavaScript
error isn't triggered when a subscription has no acquisition details.

To test, apply the patch and go to Serials.

 - Locate a subscription which isn't tied to acquisitions. In the
   browser console there should be no errors.
 - Locate a subscription which is part of an order. There should be an
   'Acquisitions details' tab and the order information on that tab
   should be displayed as a collapsible tree.

Signed-off-by: Charles Farmer <charles.farmer@inLibro.com>

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>