Bug 22360: (bug 21205 follow-up) Restore OPACAcquisitionDetails behavior

Bug 22360: (bug 21205 follow-up) Restore OPACAcquisitionDetails behavior

Caused by
  commit 7d10549ae8632e6640d3a99014268a2a1e46b3c4
  Bug 21205: Replace C4::Items::GetOrderFromItemnumber calls

At this point $order is a Koha::Acquisition::Order object, not a hashref
anymore.

Test plan:
Create an order, receive items
Enable OPACAcquisitionDetails
At the detail page of the bibliographic record you should see
"X items are on order." at the bottom of the items list

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>