wallet: Fix possible memory leak in CreateWalletFromFile.

If there was an error loading the wallet after creating the instance,
the instance would leak. This uses RAII to ensure the instance is
cleaned up in that case.

src/wallet/wallet.cpp

@@ -3947,7 +3947,7 @@ CWallet* CWallet::CreateWalletFromFile(const std::string& name, const fs::path&
 
     int64_t nStart = GetTimeMillis();
     bool fFirstRun = true;
-    CWallet *walletInstance = new CWallet(name, WalletDatabase::Create(path));
+    std::unique_ptr<CWallet> walletInstance = MakeUnique<CWallet>(name, WalletDatabase::Create(path));
     DBErrors nLoadWalletRet = walletInstance->LoadWallet(fFirstRun);
     if (nLoadWalletRet != DBErrors::LOAD_OK)
     {
@@ -4058,9 +4058,6 @@ CWallet* CWallet::CreateWalletFromFile(const std::string& name, const fs::path&
             pindexRescan = FindForkInGlobalIndex(chainActive, locator);
     }
 
-    walletInstance->m_last_block_processed = chainActive.Tip();
-    RegisterValidationInterface(walletInstance);
-
     if (chainActive.Tip() && chainActive.Tip() != pindexRescan)
     {
         //We can't rescan beyond non-pruned blocks, stop and throw an error
@@ -4089,7 +4086,7 @@ CWallet* CWallet::CreateWalletFromFile(const std::string& name, const fs::path&
 
         nStart = GetTimeMillis();
         {
-            WalletRescanReserver reserver(walletInstance);
+            WalletRescanReserver reserver(walletInstance.get());
             if (!reserver.reserve()) {
                 InitError(_("Failed to rescan the wallet during initialization"));
                 return nullptr;
@@ -4134,7 +4131,11 @@ CWallet* CWallet::CreateWalletFromFile(const std::string& name, const fs::path&
         LogPrintf("mapAddressBook.size() = %u\n",  walletInstance->mapAddressBook.size());
     }
 
-    return walletInstance;
+    walletInstance->m_last_block_processed = chainActive.Tip();
+
+    CWallet* wallet_raw_ptr = walletInstance.release();
+    RegisterValidationInterface(wallet_raw_ptr);
+    return wallet_raw_ptr;
 }
 
 std::atomic<bool> CWallet::fFlushScheduled(false);