Always return 'id' key in the read result

The 'id' should not be removed from the result if a field use it as an extra
(e.g. for context).

issue8470
review263841002

trytond/model/modelsql.py

@@ -704,6 +704,7 @@ class ModelSQL(ModelStorage):
                 extra_fields.add(field.datetime_field)
             if field.context:
                 extra_fields.update(fields.get_eval_fields(field.context))
+        extra_fields.discard('id')
         all_fields = (
             set(fields_names) | set(fields_related.keys()) | extra_fields)