Nanocat discards the reply from the REP socket.

```
nanocat --rep --bind tcp://127.0.0.1:1234 --data pong --format ascii
nanocat --req --connect tcp://127.0.0.1:1234 --data ping --format ascii
```
I guess because the socket is already in a closed state after the server sends its reply, the client never outputs the 'pong' message.

The attached commit fixes the problem, but since I'm new to nanomsg I don't know if this is the appropriate way to solve the issue.