Assistant does not load page when different page is missing

1. Start Assistant.
2. In the "Contents" view:
   1. Click on "Qt Assistant Quick Guide".
   2. Click on "Qt 3D".
      That page is being shown, so it must be there.
   3. Click on "Qt 3D Core".
      That page, can't be found, see QTBUG-67669.
   4. Click on "Qt 3D" again.
      Assistant does not even try to load the page. The error message from the previous step does not change.

When clicking on an entry in the "Contents" view, that page should be loaded regardless of which page or error message was shown before.