Bug 31154: Avoid unecessary loop

We don't need to loop over the subfield and enter this block if there is
no record.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>

Koha/UI/Form/Builder/Item.pm

@@ -152,7 +152,8 @@ sub generate_subfield_form {
         && !$value
         && $subfield->{kohafield}
         && $subfield->{kohafield} eq 'items.itemcallnumber'
-        && $pref_itemcallnumber )
+        && $pref_itemcallnumber
+        && $marc_record )
     {
         foreach
           my $pref_itemcallnumber_part ( split( /,/, $pref_itemcallnumber ) )
@@ -162,7 +163,7 @@ sub generate_subfield_form {
             my $CNsubfields =
               substr( $pref_itemcallnumber_part, 3 );    # Any and all subfields
             $CNsubfields = undef if $CNsubfields eq '';
-            my $temp2 = $marc_record ? $marc_record->field($CNtag) : undef;
+            my $temp2 = $marc_record->field($CNtag);
 
             next unless $temp2;
             $value = $temp2->as_string( $CNsubfields, ' ' );