Description:
------------
The second AppendIterator::append() call goes endless loop when its first iterator is SplFileObject whose file has only 1 line.

Reproduce code:
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<?php

$ap = new AppendIterator();
$it = new SplFileObject('data://text/plain;base64,MA==', 'r'); // "0"
$ap->append($it);
$ap->append(new ArrayIterator(array(1))); // endless

foreach ($ap as $value) {
  var_dump($value);
};

Expected result:
----------------
string(1) "0"
int(1)

Actual result:
--------------
run endless.