fixed undefined variable

Author: paveljanda

assets/datagrid-instant-url-refresh.js

@@ -1,6 +1,6 @@
 var dataGridRegisterAjaxCall;
 
-if (naja) {
+if (typeof naja !== "undefined") {
 	dataGridRegisterAjaxCall = function (params) {
         var method = params.type || 'GET';
         var data = params.data || null;

assets/datagrid-spinners.js

@@ -1,6 +1,6 @@
 var dataGridRegisterExtension;
 
-if (naja) {
+if (typeof naja !== "undefined") {
 	dataGridRegisterExtension = function (name, extension) {
 		var init = extension.init;
 		var success = extension.success;

assets/datagrid.js

@@ -1,6 +1,6 @@
 var dataGridRegisterExtension, dataGridRegisterAjaxCall, dataGridLoad;
 
-if (naja) {
+if (typeof naja !== "undefined") {
 	dataGridRegisterExtension = function (name, extension) {
 		var init = extension.init;
 		var success = extension.success;