Bug 28213: Prevent crash if patron or club deleted after search to hold

Bug 28213: Prevent crash if patron or club deleted after search to hold

Deleting a patron or patron club causes server error on searching.

To recreate:
- create a club template
- create a club
- enroll a patron in the club
- from the clubs page, select Search To Hold for your club
- do a search, see that it says "Hold for [club name]" in your search results page
- go back to the clubs page and delete your club
- try to perform a search
=> Without this patch you get "Can't call method "name" on an undefined value at /kohadevbox/koha/catalogue/search.pl line 207"

Same when placing a hold for a patron (check the search result and the
detail pages)

Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>