Bug 23530: Fix cart showing only hidden items

Bug 23530: Fix cart showing only hidden items

Items hidden with the OpacHiddenItems system preference
were still displayed in the OPAC cart and the normal items
were hidden instead. This patch corrects the display.

To test:
- prep a test bib with hidden and other items using
  the OpacHiddenItems system preference
- add bib to cart
- observe that hidden items are displayed - non-hidden items are hidden
- apply patch, reload page
- observe that hidden items are hidden, non-hidden items are displayed

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>