gui: Use wallet name for wallet migration rather than WalletModel

To prepare for migrating wallets that are not loaded, when migration
occurs in the GUI, it should not rely on a WalletModel existing.

Co-authored-by: furszy <matiasfurszyfer@protonmail.com>

src/wallet/interfaces.cpp

@@ -652,6 +652,21 @@ public:
         };
         return out;
     }
+    bool isEncrypted(const std::string& wallet_name) override
+    {
+        auto wallets{GetWallets(m_context)};
+        auto it = std::find_if(wallets.begin(), wallets.end(), [&](std::shared_ptr<CWallet> w){ return w->GetName() == wallet_name; });
+        if (it != wallets.end()) return (*it)->IsCrypted();
+
+        // Unloaded wallet, read db
+        DatabaseOptions options;
+        options.require_existing = true;
+        DatabaseStatus status;
+        bilingual_str error;
+        auto db = MakeWalletDatabase(wallet_name, options, status, error);
+        if (!db) return false;
+        return WalletBatch(*db).IsEncrypted();
+    }
     std::string getWalletDir() override
     {
         return fs::PathToString(GetWalletDir());