Bug 19692: fix unclosed div in opac-shelves.tt

Bug 19692: fix unclosed div in opac-shelves.tt

Test plan:
1. set syspref OpacKohaUrl to "Show"
2. Log into the OPAC
3. /cgi-bin/koha/opac-shelves.pl
4. Notice that "Powered by Koha" is not in the footer in this page.
  When on the other tabs it's in the footer (out of .main)
5. Apply this patch
6. Notice that "Powered by Koha" now in the footer in the "your lists" page

Signed-off-by: Dominic Pichette <dominic@inlibro.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>