Ensure that every case.law case that we add has an opinion object (or some other solution)

[mlissner]

In #1167 we identified that when case.law cases lack bodies, we don't add Opinion objects to the DB for them. This is fine and we fixed it for tax cases, but after we add the whole corpus we should go through and check if this is an ongoing concern. Do we have clusters with no Opinion objects associated? If so, how do we resolve them?