message: use checked_sub for peekn_extra
diff: @@ -240,14 +240,11 @@ impl State {
  &self,
  n: usize,
  ) -> Result<&[(BasicValueEnum, ExtraInfo)], BinaryReaderError> {
  - if self.stack.len() < n {
  - return Err(BinaryReaderError {
  + let new_len = self.stack.len().checked_sub(n).ok_or(BinaryReaderError {
  message: "invalid value stack",
  offset: -1isize as usize,
  - });
  - }
  + })?;
  - let new_len = self.stack.len() - n;
  Ok(&self.stack[new_len..])
  }
  