fix: check if client connected when reconnecting (#1162)

This fixes Bug #1152, where calling reconnect can cause endless connect/disconnect loop.

lib/client.js

@@ -783,6 +783,7 @@ MqttClient.prototype.unsubscribe = function () {
  *
  * @returns {MqttClient} this - for chaining
  * @param {Boolean} force - do not wait for all in-flight messages to be acked
+ * @param {Object} opts - added to the disconnect packet
  * @param {Function} cb - called when the client has been closed
  *
  * @api public
@@ -929,8 +930,13 @@ MqttClient.prototype.reconnect = function (opts) {
 MqttClient.prototype._reconnect = function () {
   debug('_reconnect: emitting reconnect to client')
   this.emit('reconnect')
-  debug('_reconnect: calling _setupStream')
-  this._setupStream()
+  if (this.connected) {
+    this.end(() => { this._setupStream() })
+    debug('client already connected. disconnecting first.')
+  } else {
+    debug('_reconnect: calling _setupStream')
+    this._setupStream()
+  }
 }
 
 /**