message: fix auction Error conversion failure
diff: @@ -141,6 +141,9 @@ impl TryFrom<u8> for Error {
  d if d == Error::MissingDelegations as u8 => Ok(Error::MissingDelegations),
  d if d == Error::MismatchedEraValidators as u8 => Ok(Error::MismatchedEraValidators),
  d if d == Error::MintReward as u8 => Ok(Error::MintReward),
  + d if d == Error::InvalidValidatorSlotsValue as u8 => {
  + Ok(Error::InvalidValidatorSlotsValue)
  + }
  _ => Err(TryFromU8ForError(())),
  }
  }
  