gui: Fix duplicate wallet showing up

The slot BitcoinGUI::addWallet can be invoked twice for the same
WalletModel due to a concurrent wallet being loaded after the first `connect()`:

```cpp
 connect(wallet_controller, &WalletController::walletAdded, this, &BitcoinGUI::addWallet);
 connect(wallet_controller, &WalletController::walletRemoved, this, &BitcoinGUI::removeWallet);

 for (WalletModel* wallet_model : m_wallet_controller->getOpenWallets()) {
     addWallet(wallet_model);
```

1 files changed, 1 insertions, 1 deletions

diff --git a/src/qt/walletframe.h b/src/qt/walletframe.h
index 156653f47d..20fad08b0e 100644
--- a/src/qt/walletframe.h
+++ b/src/qt/walletframe.h
@@ -36,7 +36,7 @@ public:
 
     void setClientModel(ClientModel *clientModel);
 
-    void addWallet(WalletModel *walletModel);
+    bool addWallet(WalletModel *walletModel);
     void setCurrentWallet(WalletModel* wallet_model);
     void removeWallet(WalletModel* wallet_model);
     void removeAllWallets();