message: fix: check `this.editor` exist before `this.editor.off` in QueryEditor
  `this.editor` might be undefined if error occured during `componentDidMount`, like
diff: @@ -193,11 +193,13 @@ export class QueryEditor extends React.Component {
  }
  componentWillUnmount() {
  + if (this.editor) {
  this.editor.off('change', this._onEdit);
  this.editor.off('keyup', this._onKeyUp);
  this.editor.off('hasCompletion', this._onHasCompletion);
  this.editor = null;
  }
  + }
  render() {
  return (
  