message: nydus-image: avoid duplicated blobs in merged fs
  If the RAFS filesystems to be merged contains common referenced blob,
  those data blob will get duplicated in the merged RAFS filesystem.
diff: @@ -153,10 +153,19 @@ impl Merger {
  }
  parent_blob_added = true;
  }
  - // TODO: this seems wrong, blobs from chunk dict will be added more than one time.
  +
  + let mut found = false;
  + for (idx, blob) in blob_mgr.get_blobs().iter().enumerate() {
  + if blob.blob_id == blob_ctx.blob_id {
  + blob_idx_map.push(idx as u32);
  + found = true;
  + }
  + }
  + if !found {
  blob_idx_map.push(blob_mgr.len() as u32);
  blob_mgr.add(blob_ctx);
  }
  + }
  if let Some(tree) = &mut tree {
  let mut nodes = Vec::new();
  