Bug 15453: Assign the correct shelfid to the download list links

 Bug 15453: Assign the correct shelfid to the download list links

Introduced by bug 14544, the shelfnumber is not correctly passed to the
template.
The shelf variable is passed to the template, to access the shelfnumber,
we need to get shelf.shelfnumber.

Test plan:
At the intranet, try to download a list.
Without this patch it won't work.

Followed test plan, works as expected.
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>
(cherry picked from commit b6ded944331173b38b81fefc817293eecd9b4672)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>