Fix a fatal in the feed handler, grotesquely

Summary: The feed handler in the IRC bot calls Conduit to render feed stories, which sometimes end up here with no user. "Fix" it. This patch is really bad but the underlying code is a mess too. Fixing this is properly is blocked on T2222/T2217. Until those land, stop fataling at least.

Test Plan: @dctrwatson confirmed this fixed things.

Reviewers: dctrwatson, btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D6497