re: #193 - Institutional objects with PDFs

* fix for institutional object displays that were failing after commit eb4a0ba552054fda2f172c2bceb3d261691369d2
** http://test.1418.eanadev.org/en/trove/record/186922737
** http://test.1418.eanadev.org/en/dpla/record/b38a358ea54c6c4f0b7dc9dc95cb0d62
** http://test.1418.eanadev.org/en/digitalnz/record/30050574