Update which lock to synchronize on when calling GetBestAnchor().

src/wallet/asyncrpcoperation_sendmany.cpp

@@ -878,7 +878,7 @@ UniValue AsyncRPCOperation_sendmany::perform_joinsplit(AsyncJoinSplitInfo & info
     std::vector<boost::optional < ZCIncrementalWitness>> witnesses;
     uint256 anchor;
     {
-        LOCK2(cs_main, pwalletMain->cs_wallet);
+        LOCK(cs_main);
         anchor = pcoinsTip->GetBestAnchor();    // As there are no inputs, ask the wallet for the best anchor
     }
     return perform_joinsplit(info, witnesses, anchor);

src/wallet/asyncrpcoperation_shieldcoinbase.cpp

@@ -279,7 +279,12 @@ void AsyncRPCOperation_shieldcoinbase::sign_send_raw_transaction(UniValue obj)
 
 
 UniValue AsyncRPCOperation_shieldcoinbase::perform_joinsplit(ShieldCoinbaseJSInfo & info) {
-    uint256 anchor = pcoinsTip->GetBestAnchor();
+    uint256 anchor;
+    {
+        LOCK(cs_main);
+        anchor = pcoinsTip->GetBestAnchor();
+    }
+
     if (anchor.IsNull()) {
         throw std::runtime_error("anchor is null");
     }