R1:a590db28b254

Fix an issue where non-ID changeset state keys were used as changeset IDs

Summary:
Ref T13519. This is a little fuzzy, but I think the workflow here is:

- View an intradiff, generating an ephemeral comparison changeset with no changeset ID. This produces a state key of "*".
- Apply "hidden" state changes to the changeset.
- View some other intradiff and/or diff view.
- The code attempts to use "*" as a changset ID?

I'm not entirely sure this is accurate; this was observed in production and I…