Bug 13939: ILS-DI function GetServices doesn't work when the item/biblio is available...

Bug 13939: ILS-DI function GetServices doesn't work when the item/biblio is available for hold for specific patron

Test plan:
1) Enable ILS DI (system preference 'ILS-DI')
2) Try to access the URL
http://<your_opac_url>/cgi-bin/koha/ilsdi.pl?service=GetServices&patron_id=<borrowernumber>&item_id=<itemnumber>
Choose the patron and item to be available for hold
You'll see an error instead of valid XML response
3) apply the patch
4) try to access the same URL, you should see valid XML response with services "title level hold" and eventually "item level hold" returned

Signed-off-by: Thomas Misilo <misilot@fit.edu>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>