In the context of an exception, #route_setting is not available.

See:

- https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/14178#note_40259442
- https://github.com/ruby-grape/grape/blob/df79bc35e43f0d5b6cbd666b587cf4640de174b8/lib/grape/middleware/error.rb#L59Signed-off-by: Rémy Coutable <remy@rymai.me>