Return status code 404 on 404 page
Return status code 404 on 404 page

The NotFoundHandler previously returned status code 200
because WriteHeader wasn't called.

sisimouto/nyaa,SandroHc/nyaa,SandroHc/nyaa,SpamNeko/nyaa,sfan5/nyaa,tomleb/nyaa,sfan5/nyaa,tomleb/nyaa,sisimouto/nyaa,SpamNeko/nyaa,tomleb/nyaa,SpamNeko/nyaa,SandroHc/nyaa,sfan5/nyaa,sisimouto/nyaa,sisimouto/nyaa,SandroHc/nyaa,sfan5/nyaa,SpamNeko/nyaa,tomleb/nyaa