message: Builder: fix builder panic issue caused by empty blob size
  Blob size should be plus blob_readahead_size of readahead files
diff: @@ -385,7 +385,7 @@ impl Builder {
  let blob_index = self.blob_table.entries.len() as u32;
  let mut blob_readahead_size = 0usize;
  - let mut blob_size = blob_readahead_size;
  + let mut blob_size = 0usize;
  let mut compress_offset = 0u64;
  let mut decompress_offset = 0u64;
  let mut blob_hash = Sha256::new();
  @@ -412,6 +412,8 @@ impl Builder {
  }
  }
  + blob_size += blob_readahead_size;
  +
  // Dump other nodes
  for node in &mut self.nodes {
  if self.readahead_files.get(&node.rootfs()).is_some() {
  