Do not fail to translate model field that does not exist

(grafted from e63effe09ce756cd0e66ad635255dedc8d807c7b)

--HG--
branch : 6.0

trytond/trytond/ir/translation.py

@@ -329,7 +329,7 @@ class Translation(ModelSQL, ModelView):
                             try:
                                 field = getattr(
                                     pool.get(record.model.model), record.name)
-                            except KeyError:
+                            except (KeyError, AttributeError):
                                 continue
                             translations[record.id] = ''
                             if ttype == 'field':