Bug 23679: fix software error when trying to transfer an unknown barcode

Bug 23679: fix software error when trying to transfer an unknown barcode

When trying to transfer an unknown barcode in
/cgi-bin/koha/circ/branchtransfers.pl you get the error :

Can't call method "itemnumber" on an undefined value at
/home/koha/src/C4/Circulation.pm line 319.

This comes from C4::Circulation::transferbook which should stop when
finding unknown barcode.

Test plan :
1) Go to /cgi-bin/koha/circ/branchtransfers.pl
2) Enter a barcode not existing in database
3) Without patch you get a software error, with patch you get a message
   saying 'No Item with barcode'
4) Enter a barcode existing in database and check transfer is OK

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
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>