Strange behavior when retrying a failed job contained in a cancelled workflow

[lukasmu]

Situation:

• There is a Workflow instance in 'cancelled' state
• The Workflow instance contains a WorkflowJob in 'failed' state
• The retry method of the WorkflowJob instance is invoked

Result:
A job is dispatched to the queue. This job appears to run just fine. However, the handle method of the job is never executed.

Idea:
Maybe it should not be allowed to start jobs at all when they belong to a Workflow instance in 'cancelled' state. In this case we might want to raise an exception (similar to the one raised when trying to call the retry method of a WorkflowJob instance that is not in a failed state).