Patch around unicode dup detection failure.

I'm not super happy with this solution and I think it deserves a closer look, but since the thread for this fizzled out, this is the patch we've been running internally to unblock ourselves.  Thread for reference: https://groups.google.com/forum/#!searchin/pants-devel/unicode$20decode/pants-devel/tx4NHhxX1fI/VRP0fzzG4C4J

Testing Done:
CI passed

Reviewed at https://rbcommons.com/s/twitter/r/615/