Fixed strange segfault

Don't know why, but this fixed a segfault issue on my tests. Maybe someone else ran into the same thing ?

```bash
$ php --version
PHP 5.3.8-2 with Suhosin-Patch (cli) (built: Aug 30 2011 09:42:22) 
Copyright (c) 1997-2011 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2011 Zend Technologies
    with Xdebug v2.0.5, Copyright (c) 2002-2008, by Derick Rethans
$ phpunit --version
PHPUnit 3.7.28 by Sebastian Bergmann.
```

Without the fix, I had this:

```bash
$ phpunit
PHPUnit 3.7.29-1-g0a32f05 by Sebastian Bergmann.

Configuration read from /var/www/lafourchette-portal/phpunit.xml

......Segmentation fault
$
```

I'm currently working on reproducing this bug without giving away all my firm's code :)