404 older-style Phame URIs properly

Summary: Ref T9968. Some of the crumb/route handling wasn't quite tight enough and could hit a fatal.

Test Plan: Hit previously-fataling URI, got a 404 instead.

Reviewers: chad

Reviewed By: chad

Subscribers: starruler

Maniphest Tasks: T9968

Differential Revision: https://secure.phabricator.com/D14747