Broken links to full size image on new `images-test` view

[laulaz]

The two links to image_view_fullscreen don't work (404) if not called on an image (plone.app.contenttypes.interfaces.IImage interface).

• plone.namedfile/plone/namedfile/test.pt

  Line 35 in 7031896

  <a href="${context_url}/image_view_fullscreen"

• plone.namedfile/plone/namedfile/test.pt

  Line 68 in 7031896

  <a class="btn btn-primary fullscreen" href="${context_url}/image_view_fullscreen"><span i18n:translate="label_click_to_view_full_image">View full-size image</span></a>

See commit ce07e8d

One can easily test that on the demo site.
I tried with a news : https://classic.demo.plone.org/en/demo/a-news-item/@@images-test

[laulaz]

cc @mauritsvanrees