message: fix panic in Key::into_seed
diff: @@ -254,7 +254,12 @@ impl Key {
  Key::AuctionInfo(era_id) => {
  // stop-gap measure until this method is removed
  let mut ret = [0u8; BLAKE2B_DIGEST_LENGTH];
  - ret.clone_from_slice(&era_id.to_le_bytes());
  + let era_id_bytes = era_id.to_le_bytes();
  + let era_id_bytes_len = era_id_bytes.len();
  + assert!(era_id_bytes_len < BLAKE2B_DIGEST_LENGTH);
  + for i in 0..era_id_bytes_len {
  + ret[i] = era_id_bytes[i]
  + }
  ret
  }
  }
  