Bug 28673: Add missing ampersand to amp; construction

Bug 28673: Add missing ampersand to amp; construction

Super trivial one character fix ;)

Test plan:
Open Your Lists from the button on main page.
Click again on Your lists under Lists in the middle of the form.
Verify that the URL does no longer show something like:
    op=listamp;category=1

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>