fix (subscribe): re-subscribe if already subscribed

[bradrees]

Fixes the issue where the client goes into sleep and cannot reconnect without a full reload. Noticeable on iOS and Electron

Fixes #141

[palkan]

I'm not sure my attached PR fixes anything related to this issue, although it does prevent that 'Already subscribed' message from showing up.

Yeah, I don't think we fix the problem here; just hiding symptoms.
Sending subscribe commands when the connection's state already includes this subscription is a client-side misbehavior. We should dig this way.