Fixed buffer over-read while logging invalid request headers. Since 667aaf61a778 (1.1.17) the ngx_http_parse_header_line() function can return NGX_HTTP_PARSE_INVALID_HEADER when a header contains NUL character. In this case the r->header_end pointer isn't properly initialized, but the log message in ngx_http_process_request_headers() hasn't been adjusted. It used the pointer in size calculation, which might result in up to 2k buffer over-read. Found with afl-fuzz.