Bug 28921: Remove warning from html_helpers.inc

Bug 28921: Remove warning from html_helpers.inc

Argument "" isn't numeric in numeric gt (>) at /home/koha/src/koha-tmpl/opac-tmpl/bootstrap/en/includes/html_helpers.inc line 23.

To test:
1 - Open OPAC main page
2 - Check opac-error.log or plack-opac-error.log for message as above
3 - Apply patch
4 - Open OPAC main page
5 - Check opac-error.log again, there should be no more warnings

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>