Description:
------------
AppendIterator will iterate over iterators that you append to it during the call to append(). Expected behavior is to only iterate over attached iterators when the outer AppendIterator is iterated over.

Possibly related to https://bugs.php.net/bug.php?id=49104

Test script:
---------------
(new \AppendIterator())->append(
	new \CallbackFilterIterator(
		new \ArrayIterator([1]), 
		static function(){ echo "Iterated over"; }
	)
);

Expected result:
----------------
No output

Actual result:
--------------
"Iterated over"