The Varlamore Envoy is a quest item which, while having a known location
in the library once a rotation is determined, cannot be found under
certain circumstances. (when the Depths of Despair quest has not been
started, has been collected while completing the quest, and after the
quest is completed) Previously searching a bookcase which could contain
this book and not finding it would cause a state reset. This commit
keeps those null finds from resetting the known library state.
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