gui: fix crash when closing wallet

The crash occurs because 'WalletController::removeAndDeleteWallet' is called
twice for the same wallet model: first in the GUI's button connected function
'WalletController::closeWallet', and then again when the backend emits the
'WalletModel::unload' signal.

This causes the issue because 'removeAndDeleteWallet' inlines an
erase(std::remove()). So, if 'std::remove' returns an iterator to the end
(indicating the element wasn't found because it was already erased), the
subsequent call to 'erase' leads to an undefined behavior.

src/qt/walletcontroller.cpp

@@ -89,10 +89,10 @@ void WalletController::closeWallet(WalletModel* wallet_model, QWidget* parent)
     box.setDefaultButton(QMessageBox::Yes);
     if (box.exec() != QMessageBox::Yes) return;
 
-    // First remove wallet from node.
+    // Once the wallet is successfully removed from the node, the model will emit the 'WalletModel::unload' signal.
+    // This signal is already connected and will complete the removal of the view from the GUI.
+    // Look at 'WalletController::getOrCreateWallet' for the signal connection.
     wallet_model->wallet().remove();
-    // Now release the model.
-    removeAndDeleteWallet(wallet_model);
 }
 
 void WalletController::closeAllWallets(QWidget* parent)