make sure subject is set even if data on form is not set on build time

Currently the subject is not set for sonata_type_admin admins since the CRUDController first creates the form and sets the data afterwards. Note that this also always sets the admin, even if it has been set before.

see https://github.com/sonata-project/SonataAdminBundle/pull/1710
and https://github.com/sonata-project/SonataAdminBundle/issues/1568

Feedback welcome!