fix isRequiredSubscribeOnCurrentThread

[TORISOUP]

isRequiredSubscribeOnCurrentThread is not working. CurrentThreadScheduler is never used, even if this flag is true.

Observable.Create<int>(o =>
    {
        o.OnNext(1);
        o.OnCompleted();
        return Disposable.Empty;
    }, isRequiredSubscribeOnCurrentThread: true) // not work
    .Repeat()
    .Take(1)
    .Subscribe(x => Debug.Log(x), () => Debug.Log("Stop"))
    .AddTo(this);