Fix request #7280: artifact images slideshow shows each one twice (both hidden and displayed versions)

Change-Id: Idc6ae11a8cc051024d0617c0f8708edcff60c721
Merge commit 'refs/changes/17/2817/1' of ssh://gerrit.tuleap.net:29418/tuleap into tuleap-stable-master

* ssh://gerrit.tuleap.net:29418/tuleap:
  Fix request #7280: artifact images slideshow shows each one twice (both hidden and displayed versions)
Tuleap 7.3.99.30

Change-Id: Ia23ad497ea65ad359a1818b568636a5a7613c032