Bug 25293: Don't call escapeHtml on null

Bug 25293: Don't call escapeHtml on null

 Test Plan:

    1) Create two Checkouts
    2) view patron's checkout list
       cgi-bin/koha/members/moremember.pl?borrowernumber=pp <show
       checkout>
    3) in mysql shell delete a checkout home branch: update items set
       homebranch = null where itemnumber = xx;
    4) view patron's checkout list, again

    Without this patch the list is empty.

    Same if biblio title is null (update biblio set title = null where
    biblionumber = yy;).
    Javascript error:
    TypeError: oObj.title is null

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>