message: fix mulassign impl
diff: @@ -1029,7 +1029,7 @@ impl MulAssign<u128> for BigUint {
  if other == 0 {
  self.data.clear();
  } else if other <= BigDigit::max_value() as u128 {
  - *self *= other
  + *self *= other as BigDigit
  } else {
  let (hi, lo) = big_digit::from_doublebigdigit(other);
  *self = mul3(&self.data[..], &[lo, hi])
  