Fixes#14595.
Invalid HTTP requests could end up in an unhandled exception in
skip_200_and_304 due the record not having the status_code attribute
set. With this change we'll avoid the exception
Example:
curl -X POST -H 'Transfer-Encoding : chunked' --data-binary 'a' 'http://zulipdev.com:9991/json/messages/57'
2020-04-21 10:56:22.007 WARN [django.server] "POST /json/messages/57 HTTP/1.1" 405 95
2020-04-21 10:56:22.007 INFO [django.server] code 400, message Bad request syntax ('a')
2020-04-21 10:56:22.008 WARN [django.server] "a" 400 -
ec6022a186