erp5_json_editor: properly implement checkValidity

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

@@ -420,9 +420,9 @@
       return form_data;
     })
     .declareMethod('checkValidity', function () {
-      if (this.state.errors !== undefined) {
-        return this.state.errors.length === 0;
-      }
+      if (this.editor === undefined) {
         return true;
+      }
+      return isEmpty(this.editor.validate());
     });
 }(window, rJS, RSVP, JSONEditor, domsugar, JSON, $RefParser, URL));
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