message: nydus-image: only validate inode size when it's regular file
  Because root dir's size is zero before gathering prefetching files.
diff: @@ -123,7 +123,11 @@ impl Prefetch {
  let index = node.index;
  let mut remove_node = false;
  - if self.policy == PrefetchPolicy::None || self.disabled || node.inode.size() == 0 {
  + // Newly created root inode of this rafs has zero size
  + if self.policy == PrefetchPolicy::None
  + || self.disabled
  + || (node.inode.is_reg() && node.inode.size() == 0)
  + {
  return;
  }
  