lintian tab in work request shows a summary when the underlying artifact is gone

https://debusine.freexian.com/freexian/elts/work-request/17334/ is an example of this. The underlying artifact has expired, the work request is marked as failed because the original artifact did report some lintian errors. But the current view shows a summary without any error instead of being explicit that it can't show any detail because the artifact is gone.

In fact, we might want to drop the "Lintian" tab in that case because we really have nothing to show anymore.