message: Simplify func(&mut **iterator)
diff: @@ -328,7 +328,7 @@ where
  {
  let b = get_context_data_mut::<S, Q>(ctx);
  match b.iterators.get_mut(&iterator_id) {
  - Some(iterator) => func(&mut **iterator),
  + Some(iterator) => func(iterator),
  None => Err(VmError::iterator_does_not_exist(iterator_id)),
  }
  }
  