Bug 7338: Follow up: show link only when there is more than 1 subscription

Bug 7338: Follow up: show link only when there is more than 1 subscription

To be tested together with
http://bugs.koha-community.org/bugzilla3/attachment.cgi?id=6690

1) Create a subscription for a title
- check the link 'Show any subscription...' doesn't show now
- check the serials collection page works correctly and shows all
necessary information

2) Create a second subscription for the same title
- check a new link 'Show any subscription...' shows up now
- use links in the issue table to change between viewing the single subscription
and the overview page
- check it works correctly and all information shows up

Signed-off-by: Frédéric Demians <f.demians@tamil.fr>
It works. With this patch, on Serials Collection page, the link, 'See any
subscription attached to this biblio' appears only when there are more than one
subscription attached to the biblio record.