message: Tidy up DiversifierIndex::increment()
diff: @@ -286,19 +286,15 @@ impl DiversifierIndex {
  }
  pub fn increment(&mut self) -> Result<(), ()> {
  - let mut k = 0;
  - loop {
  + for k in 0..11 {
  self.0[k] = self.0[k].wrapping_add(1);
  if self.0[k] != 0 {
  // No overflow
  return Ok(());
  }
  - // Overflow
  - k += 1;
  - if k == 11 {
  - return Err(());
  - }
  }
  + // Overflow
  + Err(())
  }
  }
  