fix: no job start time case

[jerr]

In some cases, the job has no start time (Job.Status.StartTime = nil).
We keep the pointer values ​​and display <unknown> in the case of nil thanks to timestamp.IsZero()

func (t *Time) IsZero() bool {
	if t == nil {
		return true
	}
	return t.Time.IsZero()
}

Fixes: #87

[dalehamel]

Thanks @jerr - haven't been able to reproduce the bug with this PR.

@leodido @fntlnz what unit tests should be covered by this? What should the testing practices be for regressions like this?

I'll merge to fix this bug, but maybe we should cut a separate issue to document testing (unless there is some docs already, haven't looked too hard)

[dalehamel]

Thanks!

[fntlnz]

Thanks @jerr this looks very good!