When exporting in an iframe the whole application using the Widgetize feature, when users try to export a report's data, they click on "Export this dataset in other formats" which generates JS error "TypeError: dataTable is undefined".

Steps to reproduce

as reported by a customer:

• for example using this URL:
  https://demo.matomo.org/index.php?module=Widgetize&action=iframe&moduleToWidgetize=CoreHome&actionToWidgetize=index&idSite=62&period=week&date=yesterday
• go under a report and click export icon "Export this dataset in other formats"
• Got: JS error "TypeError: dataTable is undefined" and the popover stays on "Loading Export..."
• Expected to see the popover and choose export options, and successfully export the data.