[GH-593] Fix SimpleObjectHydrator behavior when column not exists in fieldMappings, relationMappings and metaMappings

This issue is created automatically through a Github pull request on behalf of norzechowicz:

Url: https://github.com/doctrine/doctrine2/pull/593

Message:

https://github.com/doctrine/dbal/commit/88c1975dda492f3dd93cddea71ebacb40ed7efa5 change seems to make unable to use ``findOneBy()`` method because of ``doctrine_rownum`` added to query.

``findOneBy()`` throws:

>Notice: Undefined index: doctrine_rownum in
...\vendor\doctrine\orm\lib\Doctrine\ORM\Internal\Hydration\SimpleObjectHydrator.php line 183