don't loop infinitely waiting for a user that is the site itself

src/twtxt.nim

@@ -60,7 +60,7 @@ proc getTweetsFrom*(url: string, username: string): seq[Tweet] =
 proc updateTweetsOnce*() {. gcsafe .} =
   var db = open("./data/twtxt.db", nil, nil, nil)
 
-  var users = db.getAllRows sql"select * from users"
+  var users = db.getAllRows sql"select * from users where username != 'system'"
 
   for user in users.items():
     echo "updating " & $user