message: rafs: avoid possible underflow in find_target_block()
  Avoid possible underflow in find_target_block().
diff: @@ -568,6 +568,9 @@ impl OndiskInodeWrapper {
  if h_name <= name && t_name >= name {
  return Ok(Some(pivot as usize));
  } else if h_name > name {
  + if pivot == 0 {
  + break;
  + }
  last = pivot - 1;
  } else {
  first = pivot + 1;
  