Avoid warning in Eclipselink for already flushing

[ethlo]

The class RepeatableWriteUnitOfWork is already flushing. The query will be executed without further changes being written to the database. If the query is conditional upon changed data the changes may not be reflected in the results. Users should issue a flush() call upon completion of the dependent changes and prior to this flush() to ensure correct results.

Attempt to avoid this by doing a conditional flush