Update CWallet::IsSpent() to check Sapling nullifiers.

src/wallet/wallet.cpp

@@ -717,6 +717,16 @@ bool CWallet::IsSpent(const uint256& nullifier) const
     pair<TxNullifiers::const_iterator, TxNullifiers::const_iterator> range;
     range = mapTxSproutNullifiers.equal_range(nullifier);
 
+    for (TxNullifiers::const_iterator it = range.first; it != range.second; ++it) {
+        const uint256& wtxid = it->second;
+        std::map<uint256, CWalletTx>::const_iterator mit = mapWallet.find(wtxid);
+        if (mit != mapWallet.end() && mit->second.GetDepthInMainChain() >= 0) {
+            return true; // Spent
+        }
+    }
+
+    range = mapTxSaplingNullifiers.equal_range(nullifier);
+
     for (TxNullifiers::const_iterator it = range.first; it != range.second; ++it) {
         const uint256& wtxid = it->second;
         std::map<uint256, CWalletTx>::const_iterator mit = mapWallet.find(wtxid);