Bug 32037: Check for existence of object before building link

Bug 32037: Check for existence of object before building link

This patch adds a check on the existence of the object and passes this to the template

I also drop a level of IF by moving to ELSIF

To test:
 1 - Enable ReturnLog amd IssueLog
 2 - Checkout an item to a patron
 3 - Return it
 4 - View 'Modification log' tab of the borrwer
 5 - Note item links, test them, they work
 6 - Delete the item
 7 - Reload and try links again, they do not work
 8 - Apply patch
 9 - Reload, no more links
10 - Checkout and return another item
11 - This one has links, and they work as before

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>