php server fix bug

error message is not pointer.
fix bug
The `$file` argument passed into the function will hold a copy of the pointer to the `$file` object, which is the intended usage.

Please have a look at the PHP documentation for object references:
http://php.net/manual/en/language.oop5.references.php

This comment might also be useful for a deeper understanding of how PHP5 handles function arguments:
http://php.net/manual/en/language.oop5.references.php#101900