Apply server configuration as soon as host is known. Previously, this was done only after the whole request header was parsed, and if an error occurred earlier then the request was processed in the default server (or server chosen by SNI), while r->headers_in.server might be set to the value from the Host: header or host from request line. r->headers_in.server is in turn used for $host variable and in HTTP redirects if "server_name_in_redirect" is disabled. Without the change, configurations that rely on this during error handling are potentially unsafe if SNI is used. This change also allows to use server specific settings of "underscores_in_headers", "ignore_invalid_headers", and "large_client_header_buffers" directives for HTTP requests and HTTPS requests without SNI.