Description:
------------
splFileObject->fwrite() does not write

Reproduce code:
---------------
> ls -l foo.txt
-rwxrwxrwx 1 nobody nobody 0 Feb 10 19:25 foo.txt*

<?php
$file = new SplFileObject('foo.txt', 'w');
$file->fwrite('text123');
?>

Expected result:
----------------
> ls -l foo.txt
-rwxrwxrwx 1 nobody nobody 8 Feb 10 19:25 foo.txt*

> cat foo.txt
text123

Actual result:
--------------
> ls -l foo.txt
-rwxrwxrwx 1 nobody nobody 0 Feb 10 19:25 foo.txt*

> cat foo.txt