Reader._redistribute_rdy_state() throws UnboundLocalError if no conn is found

```
WARNING: 2014-09-23 11:51:16,803: [backend:4150] connection closed
INFO: 2014-09-23 11:51:16,803: [backend:4150] attempting to reconnect in 15.00s
ERROR: 2014-09-23 11:51:21,222: Exception in callback <bound method Reader._redistribute_rdy_state of <nsq.reader.Reader object at 0x7faed7898310>>
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/tornado/ioloop.py", line 972, in _run
    return self.callback()
  File "/usr/local/lib/python2.7/dist-packages/nsq/reader.py", line 634, in _redistribute_rdy_state
    return conn
UnboundLocalError: local variable 'conn' referenced before assignment
```