2936: improve progress bar for failed jobs

2936: improve progress bar for failed jobs

Ensure that:

* All job progress bars reflect at least one task.  If a job has no
  tasks at all (done, failed, finished, or todo) that should be
  considered a failed job, so render a progress bar as though one task
  ran and failed.

* A failed job (j[:success] == false) always shows at least one failed
  task.  If a job is marked as failed but has no failed tasks, then
  pretend there was one failed task so at least some red will appear in
  the progress bar.

Fixes #2936.