Bug 27578: Initialize searchid as blank when not populated

Bug 27578: Initialize searchid as blank when not populated

This patch simply sets the searchid to a blank string if not passed in

To test:
1 - Add a new biblio and save it
2 - Check the logs: /var/log/koha/kohadev/plack-intranet-error.log (or similar)
3 - Note warn about uninitialized value
4 - Apply patch
5 - Add a new biblio
6 - No warn

Signed-off-by: Phil Ringnalda <phil@chetcolibrary.org>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>