Update Composite.php for HHVM compatibility 

Not sure, why this issue is not founded in unittests, but I got HHVM crushed with message
```
Fatal error: Stack overflow in ...../vendor/doctrine/orm/lib/Doctrine/ORM/Query/Expr/Composite.php on line 58
```
The same issue is being reported here
https://github.com/facebook/hhvm/issues/1747

@LinuxDoku proposed quick patch, which works great for me and its in this PR.

Just in case, if you wonder what trigger this error - here is my repository function, which trigger it
```
    public function findOpenTeamTimeEntry($user)
    {
        $r = $this->createQueryBuilder("t")
            ->join("t.owner","u")
            ->where("t.dateEnd IS NULL")
            ->andWhere("u.id = :user_id")
             ->setParameter(":user_id",$user->getId())
            ->getQuery()
            ->getResult();
        if(is_array($r) && count($r)) {
            return $r[0];
        } else {
            return false;
        }
    }
```

Please don't remove this empty line.