Bug 28526: Impossible to search only zero

Bug 28526: Impossible to search only zero

In staff interface and OPAC, searching only zero leads to advanced search page.

Test plan :
1) Go to opac home page
2) Enter 0 into search field
=> Without patch you go to advanced search page
=> With patch you go to results page
3) Idem on staff interface

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>