Fix segfault when calling `some_id.id_properties_ui("propname").update()`,
i.e. call the `update()` function without any keyword arguments. In such
a case, Python passes `kwargs = NULL`, but `PyDict_Contains()` is not
`NULL`-safe.
Fix segfault when calling `some_id.id_properties_ui("propname").update()`,
i.e. call the `update()` function without any keyword arguments. In such
a case, Python passes `kwargs = NULL`, but `PyDict_Contains()` is not
`NULL`-safe.