title: 304 error when refreshing the webpage using facil.io framework
body: <p>I am new to facil.io framework. i create a simple server to load html page. when I open the local host in firefox it load  perfectly. If I refresh the  page it getting 304 message and showing the html text in the browser.</p>
  
  <pre><code>#include "http.h"
  void on_request(http_s *request);
  FIOBJ HTTP_HEADER_X_DATA;
  int main(void) {
      HTTP_HEADER_X_DATA = fiobj_str_new("X-Data", 6);
      http_listen("3000", NULL, .on_request = on_request, .log = 1);
      fio_start(.threads = 1);
      fiobj_free(HTTP_HEADER_X_DATA);
  }
  
  void on_request(http_s *request) {
      char *filepath = "index.html";
      http_set_cookie(request, .name = "my_cookie", .name_len = 9, .value = "data",
              .value_len = 4);
      http_set_header(request, HTTP_HEADER_CONTENT_TYPE,
              http_mimetype_find("txt", 3));
      http_set_header(request, HTTP_HEADER_X_DATA, fiobj_str_new("my data", 7));
      if(http_sendfile2(request, filepath, strlen(filepath), NULL, 0)) {
          http_send_error(request, 404);
          FIO_LOG_WARNING("Can't read file %s", filepath);
      }  
  }
  </code></pre>
  
  <p><strong>output :</strong></p>
  
  <pre><code>127.0.0.1 - - [Mon, 26 Apr 2020 02:39:15 GMT] "GET / HTTP/1.1" 200 3328b 252ms
  127.0.0.1 - - [Mon, 26 Apr 2020 02:39:17 GMT] "GET / HTTP/1.1" 304 -- 275ms
  </code></pre>