loading info is hid when 404 is returned

frontend-js/src/main/js/ServerConnector.js

@@ -85,6 +85,10 @@ ServerConnector.readFile = function(url, description) {
   }).then(function(result) {
     content = result;
     return self.callListeners("onDataLoadStop", description);
+  }, function(error) {
+    return self.callListeners("onDataLoadStop", description).then(function() {
+      return Promise.reject(error);
+    });
   }).then(function() {
     return content;
   });