message: Clear mempool if block fails validity check.
diff: @@ -386,6 +386,8 @@ std::unique_ptr<CBlockTemplate> BlockAssembler::CreateNewBlock(const CScript& sc
  CValidationState state;
  if (!TestBlockValidity(state, chainparams, *pblock, pindexPrev, false, false)) {
  error("%s: TestBlockValidity failed: %s", __func__, FormatStateMessage(state));
  + error("%s: Clearing mempool because of error", __func__);
  + mempool.clear();
  return nullptr;
  }
  