Do not fail to clean fields from missing model from the pool

Closes #13504

trytond/trytond/ir/model.py

@@ -389,8 +389,11 @@ class ModelField(
         cursor.execute(*ir_model_field.select(
                 ir_model_field.model, ir_model_field.name, ir_model_field.id))
         for model, field, id_ in cursor:
-            Model = pool.get(model)
-            if field not in Model._fields:
+            try:
+                Model = pool.get(model)
+            except KeyError:
+                Model = None
+            if not Model or field not in Model._fields:
                 logger.info("remove field: %s.%s", model, field)
                 try:
                     cls.delete([cls(id_)])