Fix cider-connect with bencode parser

I found myself unable to connect to a running REPL after #778

The error was:

```
error in process filter: nrepl-current-connection-buffer: No nREPL connection buffer
error in process filter: No nREPL connection buffer
```

I'm not familiar with the codebase, so I don't know if this is an appropriate fix.

Anyways, thanks for coming up with this @vitoshka !
`cider-get-repl-buffer` calls `cider-current-repl-buffer` internally so I don't see what good this change will do.