- adds validateMigrationSourceDb, a read-only check that the migration source
bolt db contains at least one identity, and calls it in RaftRestoreFromBoltDb
before any streaming or bootstrap
- rejects an empty, stray, or partially-written db that db.Open would otherwise
open (creating the root bucket) and restore into an empty single-node cluster,
which os.Stat alone could not catch
- adds a unit test covering the empty and populated cases
Paul Lorenz