group with empty name breaks vibenews

[streaps]

It is possible to create a group with an empty name. The http server returns a 500 error, but the group has been created anyway. It's not possible to edit this group due to the missing name. Also vibenews does not start anymore:

$ ./vibenews vibe.db.mongo.connection.MongoDBException@/root/.dub/packages/vibe-d-0.8.4/vibe-d/mongodb/vibe/db/mongo/connection.d(472): Index keys cannot contain an empty field.