message: fix lock order
diff: @@ -131,7 +131,7 @@ std::unique_ptr<CBlockTemplate> BlockAssembler::CreateNewBlock(const CScript& sc
  pblocktemplate->vTxFees.push_back(-1); // updated at end
  pblocktemplate->vTxSigOpsCost.push_back(-1); // updated at end
  - LOCK2(cs_main, mempool.cs);
  + LOCK(cs_main);
  CBlockIndex* pindexPrev = chainActive.Tip();
  assert(pindexPrev != nullptr);
  nHeight = pindexPrev->nHeight + 1;
  