agent: launch immediately after loading for new jobs

This whole block looks better written as:

```
if cJob == nil {
    tc := newTaskChain(dJob) 		
    tc.Add(task{
        typ:    taskTypeLoadJob,
        reason: taskReasonScheduledButUnloaded,
    })

    // as an optimization, queue the job for launching immediately after loading
    if dJob.TargetState == job.JobStateLaunched {
        tc.Add(task{
            typ:    taskTypeStartJob,
            reason: taskReasonLoadedDesiredStateLaunched,
        })
    }
    return &tc
}	
```