Bug 30485: (bug 30063 follow-up) Display all patrons if not term passed

Bug 30485: (bug 30063 follow-up) Display all patrons if not term passed

Regression from bug 30063. If you are searching all patrons (not search term passed) from the header, the patron search result is not displayed.

Test plan:
Go to the Koha homepage, search patrons, don't enter a search term and
click "submit"
All patrons must be returned.
Regression test: on the other patron search forms, confirm that there is
no regression, ie. no patron displayed until you search for something

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>