Missing schema reported by Configuration Inspector.

The above patch filters the 'roles', so that no values '0' are saved (for unselected roles - which causes mentioned error)
Also, the 'days_to_trigger' validation is moved (together with above roles) to the WorkflowAbstractcNotification::save() function, so that it is checked upon save, whatever the source.

Automatically closed - issue fixed for 2 weeks with no activity.