sanity tests for vdb publish

Inspired by the Crowdstrike event, where a file containing only zeros got pushed to all users. We need some tests to prevent an empty or corrupted SQLite database from getting published to the VDB repo. We currently have a metadata file that has some [counts](https://github.com/AppThreat/vulnerability-db/blob/e0e3ec87efa18fb63c57a57c6020301add99fb0f/vdb/cli.py#L211). But best to have a range of queries based on some types, namespaces, and names.