Bug 19431: Fix error when checking out an unknown barcode

Bug 19431: Fix error when checking out an unknown barcode

It seems this has been caused by
  commit 1544f9a5d4a8acd47c97d7c6ac55dee8e759d3ff
    Bug 18276: Remove GetBiblioFromItemNumber - circulation pages

To reproduce the problem you need switch on the two prefs
 - OnSiteCheckouts
 - OnSiteCheckoutsForce

Test plan:
Try to check an item out using an unknown barcode
With the 2 prefs set to on and without this patch, you will get the
following error in the log

  Can't call method "materials" on an undefined value at
  /home/vagrant/kohaclone/circ/circulation.pl line 387.

With this patch applied you should not get this error and a correct
behaviour for the different pref combinations.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>