Bug 20687: Check all share keys for a given list

Bug 20687: Check all share keys for a given list

This patch gets all the shares for a list and iterates through to find
the correct one when accepting from a link

To test:
1 - Create a private list in the opac
2 - Invite 2 patrons to the list
3 - Try to accept from the patron you first shared to
4 - You will get a failure message about expiration of the link
5 - Apply patch
6 - Now try to accept the first share
7 - It works! Success!

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>