rails/event: log zero status codes
rails/event: log zero status codes

This is going to be helpful in troubleshooting #991.
(Airbrake: got status_code=0, wanted >=200 and <600)

I am currently not sure why this happens and I hope to collect more debug
information.

airbrake/airbrake,nick-desteffen/airbrake,airbrake/airbrake,nick-desteffen/airbrake