Bug 23117: Shortcut additem.pl on nonexistent biblionumber

Bug 23117: Shortcut additem.pl on nonexistent biblionumber

To prevent additem.pl to crash when called with a nonexistent
biblionumber we are here implementing the blocking_error.inc trick to
display a friendly message instead.

Can't call method "fields" on an undefined value at
/home/vagrant/kohaclone/cataloguing/additem.pl line 736.

Test plan:
hit
/cataloguing/additem.pl?biblionumber=
/cataloguing/additem.pl?biblionumber=424242
You will get a friendly "Bibliographic record not found." message,
instead of a 500

Signed-off-by: Bin Wen <bin.wen@inlibro.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>