Fix crash in onerror (#117)

Fixes #116

Author: dotchev

lib/protocol/Connection.js

@@ -226,7 +226,7 @@ Connection.prototype._addListeners = function _addListeners(socket) {
   socket.on('data', ondata);
 
   function onerror(err) {
-    var cb = self._state.receive;
+    var cb = self._state && self._state.receive;
     if (cb) {
       self._state.receive = null; // a callback should be called only once
       cb(err);