Bug 31516: Add error message for viewing enrollments for a non-existent club

Bug 31516: Add error message for viewing enrollments for a non-existent club

To test:
 1) Go to non-existent club's enrollment page, e.g.
    http://localhost:8081/cgi-bin/koha/clubs/club-enrollments.pl?id=1010101001000
 2) Notice the not fully filled header text and empty table
 3) Apply patch and revisit the page to see the proper error message given

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>