request.path_parameters encoding at the point they're set
Check for any non-UTF8 characters in path parameters at the point they're set in
(Lots of PRs today - Rails 5 bump coincided with pen testing at GoCardless, so we're surfacing lots of edge cases!)
Check for any non-UTF8 characters in path parameters at the point they're set in `env`. Previously they were checked for when used to get a controller class, but this meant routes that went directly to a Rack app, or skipped controller instantiation for some other reason, had to defend against non-UTF8 characters themselves.