message: handle the null case
diff: @@ -204,9 +204,11 @@ pub fn unlink(path: *const c_char) -> c_int {
  pub fn waitpid(pid: pid_t, stat_loc: *mut c_int, options: c_int) -> pid_t {
  unsafe {
  - let mut temp: usize = *stat_loc as usize;
  - let res = e(syscall::waitpid(pid as usize, &mut temp, options as usize));
  + let mut temp: usize = 0;
  + let mut res = e(syscall::waitpid(pid as usize, &mut temp, options as usize));
  + if !stat_loc.is_null() {
  *stat_loc = temp as c_int;
  + }
  res
  }
  }
  