Make sure we have a connection before disconnecting

Author: tusbar

lib/index.js

@@ -69,7 +69,9 @@ Modulestore.prototype.detachConnection = function () {
 };
 
 Modulestore.prototype.disconnect = function () {
-    return this.connection.closeAsync();
+    if (this.connection) {
+        return this.connection.closeAsync();
+    }
 };
 
 Modulestore.prototype.listCourses = function (filter, options) {