Handle duplicate barcodes

[MagnusEnger]

What happens, and what should happen, when you receive an ILL and try to add a barcode that already exists in Koha?

            # Set a barcode, if one was supplied
            my $barcode = $params->{other}->{ill_barcode};
            if ( $barcode ) {
                my $item = Koha::Items->find({ 'biblionumber' => $request->biblio_id });
                if ( $item->barcode ) {
                    warn "Item already has barcode: " . $item->barcode;
                } else {
                    $item->barcode( $barcode );
                    $item->store;
                }
            }