Representation Thumbnails Only Work When Primary is 1st

[miqrogroove]

When the primary representation isn't sorted to the top of the rep list, the thumbnails on the object details page exhibit off-by-one behavior.

I fixed this on the master branch a year or two ago. It still needs to be fixed on dev/php8.

[miqrogroove]

I have a patch for this now, but I'm having trouble testing it because in some situations the thumbnail count is not equal to the slide count. I will investigate.