query.stream()._read without connection is a no-op

Fixes errors when `.stream()` is called on a query without a
connection (e.g. a query created using `createQuery`).

Author: grncdr

lib/protocol/sequences/Query.js

@@ -193,7 +193,7 @@ Query.prototype.stream = function(options) {
   stream = new Readable(options);
 
   stream._read = function() {
-    self._connection.resume();
+    self._connection && self._connection.resume();
   };
 
   this.on('result',function(row,i) {