Islandora thumbnail URLs not generating properly

[lfinnigan]

Maybe due to work to fix Historic Pittsburgh, Islandora thumbnails are now not generating properly.

Institutions: Library Company, American Philosophical Society, Presbyterian Historical Society

Example:
http://test.padigital.org/catalog/dplapa:LIBCO_Islandora_3536

The second identifier (thumbnail) is: https://digital.librarycompany.org/islandora/object/https://digital.librarycompany.org/islandora/object/Islandora%3A3536

It should be:
https://digital.librarycompany.org/islandora/object/Islandora%3A3536/datastream/TN/view/

Which is the trackback URL (first value in identifier) + /datastream/TN/view/

Some of the collections affected are in production already. A contributor asked us to reharvest them to get updated/added records, but we won't be able to reharvest them without a fix for this.