erp5_json_editor: Disable ajax and catch promise

See merge request !1858

bt5/erp5_json_editor/SkinTemplateItem/portal_skins/erp5_json_editor/json-editor.gadget.js.js

@@ -221,7 +221,7 @@
         .push(function (schema) {
           return new JSONEditor(domsugar(json_editor_container), {
             schema: schema,
-            ajax: true,
+            ajax: false,
             theme: 'bootstrap5',
             show_errors: 'always',
             //iconlib: 'fontawesome5',
@@ -245,11 +245,11 @@
           gadget.editor = editor;
           gadget.editor.on('change', gadget.deferNotifyChangeBinded.bind(gadget));
 
-          // return complex object is not possible throught iframe
-          // it seems to crash rjs somewhere. To check...
-          // https://lab.nexedi.com/nexedi/renderjs/blob/master/renderjs.js#L2070
-          //return editor;
-        });
+          // editor relies on async load function, so we must return the promise
+          // to finish before continue, otherwise rendering errors wont throw Errors 
+          // in the same stack as expected.
+          return editor.promise
+        })
     })
     .declareMethod('getContent', function () {
       var form_data = {};