Update a couple permissions things, no longer allow anonymous users.

diskwriter/diskwriter.go

@@ -196,6 +196,9 @@ func (client *Client) PushConn(g *hall.Hall, id string, up conn.Up, tracks []con
 		g.WallOps("Write to disk: " + err.Error())
 		return err
 	}
+	if down == nil {
+		return nil
+	}
 
 	client.down[up.Id()] = down
 	return nil
@@ -699,7 +702,7 @@ func newDiskConn(client *Client, up conn.Up, remoteTracks []conn.UpTrack) (*disk
 	}
 
 	if len(tracks) == 0 {
-		return nil, errors.New("no usable tracks found")
+		return nil, nil
 	}
 
 	down := &diskConn{