fix preview js

public/js/app.js

@@ -55,7 +55,7 @@ var Gogits = {};
         toggleShow: function () {
             $(this).removeClass("hidden");
         },
-        toggleAjax: function (successCallback) {
+        toggleAjax: function (successCallback, errorCallback) {
             var url = $(this).data("ajax");
             var method = $(this).data('ajax-method') || 'get';
             var ajaxName = $(this).data('ajax-name');
@@ -91,6 +91,7 @@ var Gogits = {};
                 url: url,
                 method: method.toUpperCase(),
                 data: data,
+                error: errorCallback,
                 success: function (d) {
                     if (successCallback) {
                         successCallback(d);
@@ -527,6 +528,8 @@ function initIssue() {
             var $this = $(this);
             $this.toggleAjax(function (resp) {
                 $($this.data("preview")).html(resp);
+            },function(){
+                $($this.data("preview")).html("no content");
             })
         });
         $('.issue-write a[data-toggle]').on("click", function () {
@@ -574,9 +577,9 @@ function initRelease() {
         $('[data-ajax-name=release-preview]').on("click", function () {
             var $this = $(this);
             $this.toggleAjax(function (json) {
-                if (json.ok) {
+                $($this.data("preview")).html(json.ok ? json.content : "no content");
-                    $($this.data("preview")).html(json.content);
+            }, function () {
-                }
+                $($this.data("preview")).html("no content");
             })
         });
         $('.release-write a[data-toggle]').on("click", function () {