message: Returned protected scope for callbacks property of Event for SurveyPDF
diff: @@ -1449,7 +1449,7 @@ export class SurveyElement extends Base implements ISurveyElement {
  export class Event<T extends Function, Options> {
  public onCallbacksChanged: () => void;
  - private callbacks: Array<T>;
  + protected callbacks: Array<T>;
  public get isEmpty(): boolean {
  return this.callbacks == null || this.callbacks.length == 0;
  }
  