Usage reporting (analytics) break when no project exists

[ktuite]

Was just trying a fresh central database with no projects and went to check on the usage reporting. I remember wondering about this in some code review in the last few months. Sure enough, when there are no projects, /v1/analytics/preview returns a totally blank response (not even an empty array or dict) (bit also not an error) that frontend doesn't know how to render.

I believe the analytics were added before the default project was removed.

[ktuite]

The response looks better than it did before, but frontend can't handle projects being an empty array.

I'm planning to add a test to backend and I can make a quick update to frontend, too.