message: Optimize write_block
diff: @@ -228,17 +228,9 @@ impl<'a, W: Write + 'a> BitWriter<'a, W> {
  // Figure F.2
  let mut zero_run = 0;
  - let mut k = 0usize;
  -
  - loop {
  - k += 1;
  + for k in 1usize..=63 {
  if block[UNZIGZAG[k] as usize] == 0 {
  - if k == 63 {
  - self.huffman_encode(0x00, actable)?;
  - break;
  - }
  -
  zero_run += 1;
  } else {
  while zero_run > 15 {
  @@ -260,6 +252,10 @@ impl<'a, W: Write + 'a> BitWriter<'a, W> {
  }
  }
  + if block[UNZIGZAG[63] as usize] == 0 {
  + self.huffman_encode(0x00, actable)?;
  + }
  +
  Ok(dcval)
  }
  