message: add null-guard for stickerpickerWidget in StickerPicker
diff: @@ -166,6 +166,7 @@ export default class Stickerpicker extends React.Component {
  }
  _sendVisibilityToWidget(visible) {
  + if (!this.state.stickerpickerWidget) return;
  const widgetMessaging = ActiveWidgetStore.getWidgetMessaging(this.state.stickerpickerWidget.id);
  if (widgetMessaging && visible !== this._prevSentVisibility) {
  widgetMessaging.sendVisibility(visible);
  