Fix DataAccess test on HHVM

[deeky666]

HHVM expects constructor arguments to be null in PDOStatement::setFetchMode() when using \PDO::FETCH_CLASS with custom class that does not have a constructor.

PDOException: SQLSTATE[HY000]: General error: user-supplied class does not have a constructor, use NULL for the ctor_params parameter, or simply omit it

[doctrinebot]

Hello,

thank you for creating this pull request. I have automatically opened an issue
on our Jira Bug Tracker for you. See the issue link:

http://www.doctrine-project.org/jira/browse/DBAL-767

We use Jira to track the state of pull requests and the versions they got
included in.