Description:
------------
When we use reference on the object property instead of value in callback function of CallbackFilterIterator we expect that we can change this property value inside of the function, but in php 7 this functionality doesn't work.

Test script:
---------------
<?php

$data = [
    [1,2]
];

$callbackTest = new CallbackFilterIterator(new ArrayIterator($data), function (&$current) {
    $current['message'] = 'Test message';
    return true;
});

$callbackTest->rewind();
$data = $callbackTest->current();
$callbackTest->next();
var_dump($data);

Expected result:
----------------
array(3) {
  [0]=>
  int(1)
  [1]=>
  int(2)
  ["message"]=>
  string(12) "Test message"
}

Actual result:
--------------
array(2) {
  [0]=>
  int(1)
  [1]=>
  int(2)
}