xcb_request_check hangs when making a request after a flush

Minimal repro:

#include <xcb/xcb.h>
int main() {
  xcb_connection_t *connection = xcb_connect(NULL, NULL);
  xcb_void_cookie_t cookie = xcb_set_input_focus_checked(connection, 0, 0, 0);
  xcb_flush(connection);
  xcb_get_input_focus(connection);
  xcb_request_check(connection, cookie);
  return 0;
}

The xcb_request_check() hangs indefinitely because libxcb doesn't flush the get_input_focus request.