Presence.subscribe() reports success after the server rejects it #757

Summary

Presence._handleSubscribe sets subscribed = true even when the server rejects the subscription:

Presence.prototype._handleSubscribe = function(error, seq) {
  if (this.wantSubscribe) this.subscribed = true;

Doc._handleSubscribe, by contrast, returns on error before marking itself subscribed.

Repro

1. Reject ps in 'receive' middleware
2. presence.subscribe(cb): cb gets the error, but presence.subscribed is true
3. presence.subscribe(cb) again: cb is called with no error, and nothing is sent to the server
4. Reconnect: _resubscribe sends the subscription again, and its rejection is emitted as 'error' on the Presence, which throws if nothing is listening

This also means apps can't reject presence subscriptions in middleware without leaving the client in a broken state. The presence access control docs in #752 recommend filtering in 'sendPresence' for that reason.

Suggested fix

On error, leave subscribed alone and reset wantSubscribe, as Doc does, so a later subscribe() actually retries and a reconnect doesn't re-send a subscription the server already refused.