Handle items without media

[ReallyLiri]

No description provided.

[Daniel-KM]

I don't understand, the items without media are already managed (they should have an external manifest in a property). Why display the viewer without anything to show ?

[ReallyLiri]

Sorry, I should've included more description.

This change prevents Universal Viewer from being rendered on item and item set pages when there is nothing displayable.

The fix in UniversalViewer.php - While the helper already had checks for empty items and empty item sets, they ran too late, after external manifest resolution had already been attempted. This meant an item with no media could still produce a viewer if some manifest-like URL path was available upstream. The change moves the displayability checks earlier in the helper flow.

This is an actual case we encountered on our Omeka and had deployed this fix on our site.