message: Fix error checking for update linear_fees serialization
diff: @@ -86,9 +86,9 @@ impl property::Serialize for UpdateProposal {
  }
  if let Some(linear_fees) = &self.linear_fees {
  codec.put_u16(UpdateTag::LinearFee as u16)?;
  - codec.put_u64(linear_fees.constant);
  - codec.put_u64(linear_fees.coefficient);
  - codec.put_u64(linear_fees.certificate);
  + codec.put_u64(linear_fees.constant)?;
  + codec.put_u64(linear_fees.coefficient)?;
  + codec.put_u64(linear_fees.certificate)?;
  }
  codec.put_u16(UpdateTag::End as u16)?;
  Ok(())
  