SetTopicScoreParams after join a new pubsub topic

[richard-ramos]

I noticed here that if a topic has not been setup before as part of the WithPeerScore option, then the exist variable will always be false, so it seems that it isn't it possible to set the TopicScoreParams with SetTopicScoreParams for new topics after GossipSub has been instantiated.

	old, exist := ps.params.Topics[topic]
	ps.params.Topics[topic] = p

	if !exist {
		return nil
	}

Is this a bug or intended behavior? because if remove the if !exist { condition, the logic seems to work fine when joining any new pubsub topic.

[vyzo]

Hrm, i think we can call it a bug; pr welcome.