use underscore if no username found

app/Tweet.php

@@ -56,7 +56,7 @@ class Tweet extends Model
   }
 
   public function twitter_permalink() {
-    return 'https://twitter.com/'.($this->player ? $this->player->twitter : $this->author_username).'/status/'.$this->tweet_id;
+    return 'https://twitter.com/'.($this->player ? $this->player->twitter : '_').'/status/'.$this->tweet_id;
   }
 
   public static function claimed_timeout() {