Usage of modifiers in 'direct' mappings filters the field out when using map_record.values(fields=[...])

[Guewen Baconnier @ Camptocamp]

With a mapper having a modifier:

        class MyMapper(ImportMapper):
            direct = [('field', 'field2'),
                            ('no_field', 'no_field2'),
                             (convert('name', int), 'out_name')]

And such a record:

        record = {'name': '300', 'field': 'value', 'no_field': 'no_value'}

When calling the mapper with the 'fields' option to filter the fields to map:

        mapper = MyMapper(env)
        map_record = mapper.map_record(record)
        map_record.values(fields=['field', 'name'])

Expected is:

    {'out_name': 300, 'field2': 'value'}

Actual result is:

     {'field2': 'value'}

Because 'name' is shadowed by the closure function.