message: Write ExternalIterator constructor more compact
diff: @@ -84,10 +84,8 @@ impl ReadonlyStorage for ExternalStorage {
  };
  let order = order as i32;
  - let scan_result = unsafe { db_scan(start_ptr, end_ptr, order) };
  - let iter = ExternalIterator {
  - iterator_id: scan_result,
  - };
  + let iterator_id = unsafe { db_scan(start_ptr, end_ptr, order) };
  + let iter = ExternalIterator { iterator_id };
  Box::new(iter)
  }
  }
  