Ticket 77 - Null deref in ns_job_done
    
    Bug Description:  Coverity detected a potential null deref in ns_job_done where
    we did not check if job was null before we entered the monitor.
    
    Fix Description:  PR_ASSERT the job and check it's not null before we enter
    the monitor.
    
    https://pagure.io/nunc-stans/issue/77
    
    Author: wibrown
    
    Review by: nhosoi (Thanks!)