[fuzzysearch] Fix multiple selected albums refresh

When two or more duplicate images are selected via the similarities tree view, and both of them gets duplicated items removed (thus resulting in the private search album from each tree item to report a single entry); only the first tree item gets hidden, leaving the other selected items in the three view visible.

My suspicion is that setting the item to hidden messes up with the tree widget item iterator, causing every selected album that is not the first to not hide when all duplicate images are removed. Thus, switching to a predefined list of selected items resolves the issue.

I'm not familiar with digiKam codebase and it's been a while I don't contribute to KDE so please let me know if there's something else I should do :-) Thank you!