Prevent 404's from being returned as 200s

I hate this strategy. But it's a starting point. Maybe it gives
impetus for a proper fix.

/cc @zarino in case he feels like weighing in with a quick answer.

I'm guessing there might be a "put the code in the shared" thing we can do.

edit: Now tested locally, seems to work. Also resolved my "hate this strategy" qualm.

Fixes #551