Added default overwrite in error_page 494. We used to have default error_page overwrite for 495, 496, and 497, so a configuration like error_page 495 /error; will result in error 400, much like without any error_page configured. The 494 status code was introduced later (in 3848:de59ad6bf557, nginx 0.9.4), and relevant changes to ngx_http_core_error_page() were missed, resulting in inconsistent behaviour of "error_page 494" - with error_page configured it results in 494 being returned instead of 400. Reported by Frank Liu, http://mailman.nginx.org/pipermail/nginx/2020-February/058957.html.