message: utils: fix a warning generated when decoding chunk data
  The refactor introduced a regression which tries to decompress an
  uncompressed data chunk, thus generating a warning about decompression
  failure. Fix it by check whether the chunk data is compressed or not.
diff: @@ -1160,7 +1160,9 @@ impl FileCacheEntry {
  chunk.compressed_size() as u64
  };
  let mut reader = FileRangeReader::new(&self.file, offset, size);
  - if self.compressor() == compress::Algorithm::Lz4Block {
  + if !chunk.is_compressed() {
  + reader.read_exact(buffer)?;
  + } else if self.compressor() == compress::Algorithm::Lz4Block {
  let mut buf = alloc_buf(size as usize);
  reader.read_exact(&mut buf)?;
  let size = compress::decompress(&buf, buffer, self.compressor)?;
  