http_server: fix resume after socket close

Socket resume may happen on a next tick, and in following scenario:

1. `socket.resume()`
2. `socket._handle.close()`
3. `socket._handle = null;`

The `_resume` will be invoked with empty `._handle` property. There is
nothing bad about it, and we should just ignore the `resume`/`pause`
events in this case.

Same applies to the unconsuming of socket on adding `data` and/or
`readable` event listeners.

Fix: https://github.com/nodejs/node/issues/2821

PR-URL: https://github.com/nodejs/node/pull/2824


Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>