check if cb defined befire binding to domain

Author: sidorares

lib/Connection.js

@@ -21,7 +21,7 @@ function Connection(options) {
 
 function bindToCurrentDomain(cb) {
   var domain = process.domain;
-  if (!domain)
+  if (!domain || !cb)
     return cb;
   else
     return domain.bind(cb);