connection: add additional guards for idle changing

lib/Connection.js

@@ -205,7 +205,8 @@ Connection.prototype.connect = function() {
 
       if (self._queue.length === 0
           && self._config.keepalive
-          && self.state === 'authenticated') {
+          && self.state === 'authenticated'
+          && !self._idle.enabled) {
         self._idle.enabled = true;
         self._doKeepaliveTimer(true);
       }
@@ -1368,7 +1369,8 @@ Connection.prototype._resTagged = function(info) {
 
   if (this._queue.length === 0
       && this._config.keepalive
-      && this.state === 'authenticated') {
+      && this.state === 'authenticated'
+      && !this._idle.enabled) {
     this._idle.enabled = true;
     this._doKeepaliveTimer(true);
   }
@@ -1582,7 +1584,8 @@ Connection.prototype._enqueue = function(fullcmd, promote, cb) {
   } else if (this._curReq
              && this._curReq.type === 'IDLE'
              && this._sock
-             && this._sock.writable) {
+             && this._sock.writable
+             && this._idle.enabled) {
     this._idle.enabled = false;
     this.debug && this.debug('=> DONE');
     this._sock.write('DONE' + CRLF);