more than 3 topics blocks async operations

If we have more than 3 active topics Pulsar blocks all async operations such as readdir, readFile, http.get, etc. on NodeJS
So, I cannot read even static files, do HTTP requests, etc.

I prepared for you a pure NodeJS example with "Pulsar client.subscribe" and 4 topics [here](https://github.com/steelone/node_pulsar/tree/master)

Start with the linked pure NodeJS example and reproduce the problem using Pulsar client.subscribe with four topics. Trace why readdir, readFile, and http.get stop completing when more than three topics are active; done means these asynchronous operations continue to work with four or more topics.

索引モデルが issue の本文から書いたものです。