message: Skip StreamReader::read call when seek offset falls on a chunk boundary
diff: @@ -311,9 +311,11 @@ impl<R: Read + Seek> Seek for StreamReader<R> {
  // A single call to self.read() is sufficient, because we know it will
  // read a full chunk from the inner reader, and offset is always smaller
  // than a chunk.
  + if offset > 0 {
  let mut to_drop = Vec::with_capacity(offset);
  to_drop.resize(offset, 0);
  self.read(&mut to_drop)?;
  + }
  // All done!
  Ok(target_pos)
  