Bug 32639: Send opac-search.osdx without doing an empty search

Bug 32639: Send opac-search.osdx without doing an empty search

This patch sends out opac-search.osdx without running the entirety
of opac-search.pl without any search query.

This prevents unnecessary computations and warnings from appearing
in the logs.

Test plan:
1. Apply patch
2. Go to
http://kohadev.myDNSname.org:8080/cgi-bin/koha/opac-search.pl?format=opensearchdescription
3. Note that no errors appear in
/var/log/koha/kohadev/plack-opac-error.log
4. Verify that opac-search.pl still works as expected when
doing a search via the web UI

Signed-off-by: David Nind <david@davidnind.com>
JD Amended patch: remove ref to bug number, we use git!

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>