message: Add double lock for RPC function
diff: @@ -2888,7 +2888,7 @@ void CWallet::ListAvailableCoinsMintCoins(vector <COutput> &vCoins, bool fOnlyCo
  void CWallet::ListAvailableSigmaMintCoins(vector<COutput> &vCoins, bool fOnlyConfirmed) const {
  vCoins.clear();
  - LOCK(cs_wallet);
  + LOCK2(cs_main, pwalletMain->cs_wallet);
  list<CSigmaEntry> listOwnCoins;
  CWalletDB walletdb(pwalletMain->strWalletFile);
  listOwnCoins = pwalletMain->hdMintTracker->MintsAsZerocoinEntries();
  