Multi image hint bugfix

[mspalti]

Description

mirador-viewer.service has a method to determine whether or not multiple images exist in an Item's IIIF Bundles. When the image count is greater than one a "multi" query parameter is passed as a hint to the viewer. The hint can be used to modify the Mirador viewer layout (in the default mirador configuration thumbnail navigation panel is added to the right).

At some point in recent releases this stopped working and the "multi" parameter is never added, probably because switchMap is unsubscribing before the count is incremented in the inner observable.

Instructions for Reviewers

List of changes in this PR:

• Changed operators in the getImageCount() method. The original version relied only on switchMap.

If you compile the frontend in production and view an IIIF-enabled item with more than one image you should see the multi parameter in the iframe URL and see a right navigation thumbnail menu in the viewer.

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