[compare] add alert for error message

Author: waiterZen

plugins/compare/api/api.js

@@ -188,8 +188,8 @@ var exported = {},
                         });
                     });
                 },
-                function(err, res) {
-                    if (err) {
+                function(err2, res) {
+                    if (err2) {
                         return common.returnMessage(params, 503, 'Fetch apps data failed');
                     }
                     common.returnOutput(params, res);

plugins/compare/frontend/public/javascripts/countly.models.js

@@ -269,6 +269,9 @@
                 }
 
                 _appData.all.avgduration.total = (_appData.all.sessions.total === 0) ? 0 : _appData.all.duration.total / _appData.all.sessions.total;
+            },
+            error: function() {
+                window.CountlyHelpers.notify({type: 'error', message: jQuery.i18n.map['management-applications.plugins.error.server']});
             }
         });
     };