[FIX] web: export field with '/'

- Activate lots and SN
- Go to Inventory > Inventory Adjustments
- Export a record
- Select the field 'Inventories > Lot/Serial Number'

The `name_get` of the field is exported, not its XMLID.

This is because the parsing made in order to limit the depth of export
is made on the label, not on the field name.

Actually, it is not clear WHY this limitation exists, but we keep it for
compatibility purpose.

opw-1877092

addons/web/controllers/main.py

@@ -1290,7 +1290,7 @@ class Export(http.Controller):
                       'relation_field': field.get('relation_field')}
             records.append(record)
 
-            if len(name.split('/')) < 3 and 'relation' in field:
+            if len(id.split('/')) < 3 and 'relation' in field:
                 ref = field.pop('relation')
                 record['value'] += '/id'
                 record['params'] = {'model': ref, 'prefix': id, 'name': name}