Bug 12478: Remove empty limit parameter

Bug 12478: Remove empty limit parameter

If no limit are passed, the url will contain '&limit=' anyway.
It is not necessary and can be avoided easily

Test plan:
1/ Search for a term in your catalogue
2/ Hover over a link in the facet area
3/ The link is
cgi-bin/koha/opac-search.pl?idx=kw&q=your_term&limit=&limit=[...]

With this patch, the empty limit parameter does not appear.

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jesse Weaver <jweaver@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>