Bug 24166: Do not hang when displaying checkout list if barcode is not set

Bug 24166: Do not hang when displaying checkout list if barcode is not set

If a barcode is not set, there is a JS error in the log:
  TypeError: oObj.barcode is null
We should not call escapeHtml() on it if not barcode is set for a given
item.

Test plan:
Check an item out
Remove its barcode
Load the checkout list
=> Without this patch you get the "loading" popup and the table is never
displayed
=> With this patch applied you see the checkout list

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>