message: wallet: refactor: avoid duplicate lookup on `mapValue["timesmart"]`
  Also, use a named cast for converting the atoi64() result into an
  unsigned int type.
diff: @@ -217,7 +217,8 @@ public:
  const auto it_op = mapValue.find("n");
  nOrderPos = (it_op != mapValue.end()) ? atoi64(it_op->second) : -1;
  - nTimeSmart = mapValue.count("timesmart") ? (unsigned int)atoi64(mapValue["timesmart"]) : 0;
  + const auto it_ts = mapValue.find("timesmart");
  + nTimeSmart = (it_ts != mapValue.end()) ? static_cast<unsigned int>(atoi64(it_ts->second)) : 0;
  mapValue.erase("fromaccount");
  mapValue.erase("spent");
  