merge bitcoin#26005: Fix error handling (copy_file failure in RestoreWallet, and in general via interfaces)

includes:
- c3e5365

continuation of b75f1ad from dash#6733

Author: kwvg

src/wallet/interfaces.cpp

@@ -617,8 +617,12 @@ class WalletLoaderImpl : public WalletLoader
         options.create_flags = wallet_creation_flags;
         options.create_passphrase = passphrase;
         bilingual_str error;
-        util::Result<std::unique_ptr<Wallet>> wallet{MakeWallet(m_context, CreateWallet(m_context, name, /*load_on_start=*/true, options, status, error, warnings))};
-        return wallet ? std::move(wallet) : util::Error{error};
+        std::unique_ptr<Wallet> wallet{MakeWallet(m_context, CreateWallet(m_context, name, /*load_on_start=*/true, options, status, error, warnings))};
+        if (wallet) {
+            return {std::move(wallet)};
+        } else {
+            return util::Error{error};
+        }
     }
     util::Result<std::unique_ptr<Wallet>> loadWallet(const std::string& name, std::vector<bilingual_str>& warnings) override
     {
@@ -627,15 +631,23 @@ class WalletLoaderImpl : public WalletLoader
         ReadDatabaseArgs(*m_context.args, options);
         options.require_existing = true;
         bilingual_str error;
-        util::Result<std::unique_ptr<Wallet>> wallet{MakeWallet(m_context, LoadWallet(m_context, name, /*load_on_start=*/true, options, status, error, warnings))};
-        return wallet ? std::move(wallet) : util::Error{error};
+        std::unique_ptr<Wallet> wallet{MakeWallet(m_context, LoadWallet(m_context, name, /*load_on_start=*/true, options, status, error, warnings))};
+        if (wallet) {
+            return {std::move(wallet)};
+        } else {
+            return util::Error{error};
+        }
     }
     util::Result<std::unique_ptr<Wallet>> restoreWallet(const fs::path& backup_file, const std::string& wallet_name, std::vector<bilingual_str>& warnings) override
     {
         DatabaseStatus status;
         bilingual_str error;
-        util::Result<std::unique_ptr<Wallet>> wallet{MakeWallet(m_context, RestoreWallet(m_context, backup_file, wallet_name, /*load_on_start=*/true, status, error, warnings))};
-        return wallet ? std::move(wallet) : util::Error{error};
+        std::unique_ptr<Wallet> wallet{MakeWallet(m_context, RestoreWallet(m_context, backup_file, wallet_name, /*load_on_start=*/true, status, error, warnings))};
+        if (wallet) {
+            return {std::move(wallet)};
+        } else {
+            return util::Error{error};
+        }
     }
     std::string getWalletDir() override
     {