message: rpc: Prevent concurrent savemempool
diff: @@ -4766,6 +4766,9 @@ bool DumpMempool()
  std::map<uint256, CAmount> mapDeltas;
  std::vector<TxMempoolInfo> vinfo;
  + static Mutex dump_mutex;
  + LOCK(dump_mutex);
  +
  {
  LOCK(mempool.cs);
  for (const auto &i : mempool.mapDeltas) {
  