Comment 20 for bug 1774777

This turns out to be more complicated than expected. We only check the cancel flag after each library, which still leaves an annoying pause before you can place the selected component (or close the parent document).

I tried allowing the event loop of the dialog to expire on its own, but then we get back to the application's main event loop still processing the end of the add-component command and die because the SCH_BASE_FRAME has been deleted out from under us.