aliased fields from root class are not recognized als root class fields, if they're the only one

If all selected fields from the root class are aliased,
Doctrine_Query->processPendingFields() won't recognize them as fields of the table and the following exception will be thrown:
"The root class of the query (alias c) must have at least one field selected."

In my real world example, this could only be fixed, using the primary key of the root class/table in select