message: [mempool] Don't throw expected error message when upgrading
diff: @@ -4744,6 +4744,8 @@ bool LoadMempool(CTxMemPool& pool)
  pool.PrioritiseTransaction(i.first, i.second);
  }
  + // TODO: remove this try except in v0.22
  + try {
  std::set<uint256> unbroadcast_txids;
  file >> unbroadcast_txids;
  unbroadcast = unbroadcast_txids.size();
  @@ -4751,6 +4753,10 @@ bool LoadMempool(CTxMemPool& pool)
  for (const auto& txid : unbroadcast_txids) {
  pool.AddUnbroadcastTx(txid);
  }
  + } catch (const std::exception&) {
  + // mempool.dat files created prior to v0.21 will not have an
  + // unbroadcast set. No need to log a failure if parsing fails here.
  + }
  } catch (const std::exception& e) {
  LogPrintf("Failed to deserialize mempool data on disk: %s. Continuing anyway.\n", e.what());
  