Use the Symfony dispatcher correctly
Use the Symfony dispatcher correctly

* Event object as first arg (otherwise there is a notice in the logs)
* `dispatch` MUST return the event object

Signed-off-by: Christoph Wurst <7abde52c298496fa169fb750f91f213a282142af@winzerhof-wurst.at>

nextcloud/server,nextcloud/server,nextcloud/server,nextcloud/server