Have undeliverable errors on subscribe() sent to plugin error handler.

[akarnokd]

This change will make sure if the Subscriber has unsubscribed, the non-fatal error is sent to the plugin error handler at least. I.e.,

Observable.create(s -> {
    s.onError(new RuntimeException());
    throw new IllegalArgumentException();
}).subscribe();

In addition, if the original code threw RuntimeException in case the subscriber.onError() threw. I've changed this to OnErrorFailedException but not sure the original type was intentional or just left out.

[stevegury]

👍