MINOR: If an event has already happened, don't allow people to register for it.
MINOR: If an event has already happened, don't allow people to register for it.

burnbright/silverstripe-eventmanagement,burnbright/silverstripe-eventmanagement,souldigital/silverstripe-eventmanagement,silverstripe-australia/silverstripe-eventmanagement,stephenmcm/silverstripe-eventmanagement,souldigital/silverstripe-eventmanagement,registripe/registripe-core,stephenmcm/silverstripe-eventmanagement,silverstripe-australia/silverstripe-eventmanagement