Actually update spent index on DisconnectBlock (#3167)

Fixes #3166

Author: UdjinM6

src/validation.cpp

@@ -1647,6 +1647,13 @@ static DisconnectResult DisconnectBlock(const CBlock& block, const CBlockIndex*
     // move best block pointer to prevout block
     view.SetBestBlock(pindex->pprev->GetBlockHash());
 
+    if (fSpentIndex) {
+        if (!pblocktree->UpdateSpentIndex(spentIndex)) {
+            AbortNode("Failed to delete spent index");
+            return DISCONNECT_FAILED;
+        }
+    }
+
     if (fAddressIndex) {
         if (!pblocktree->EraseAddressIndex(addressIndex)) {
             AbortNode("Failed to delete address index");