Bug 35366: (bug 33948 follow-up) Fix display of old checkouts if no checkouts exist

Bug 35366: (bug 33948 follow-up) Fix display of old checkouts if no checkouts exist

Same patch as
  commit bee2b3d33ed6030b5a63d22148b9955a9897e51d
  Bug 33949: Fix display of old checkouts if no checkouts exist

But for the staff interface.

"""
If we pass an empty array from the perl controller, we retrieve an empty
string from the template, and the merge does not work.

This patch fixes the following bug:
Pick a patron without checkout history
Check them an item out and check it in
=> The table is empty, whereas it should display the item that has been
checked in.
"""

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>