Merge #835: Fix crash when closing wallet

a965f2b gui: fix crash when closing wallet (furszy)

Pull request description:

  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.

  Test Notes:
  Try closing any wallet using the toolbar button in the GUI. It will crash in master, but not here.

  Fixes bitcoin/bitcoin#30887.

ACKs for top commit:
  pablomartin4btc:
    tACK a965f2b
  jarolrod:
    ACK a965f2b
  hebasto:
    ACK a965f2b.

Tree-SHA512: c94681b95cb566f7aabd0d4fb10f797c2cea6ac569abc265e918f08e6abae3335432a0b0879372b54b2c109798ed0a4a249bf162c34add59cbd18d38a2d9660e

src/qt/walletcontroller.cpp

@@ -79,6 +79,14 @@ std::map<std::string, std::pair<bool, std::string>> WalletController::listWallet
     return wallets;
 }
 
+void WalletController::removeWallet(WalletModel* wallet_model)
+{
+    // 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();
+}
+
 void WalletController::closeWallet(WalletModel* wallet_model, QWidget* parent)
 {
     QMessageBox box(parent);
@@ -89,10 +97,7 @@ void WalletController::closeWallet(WalletModel* wallet_model, QWidget* parent)
     box.setDefaultButton(QMessageBox::Yes);
     if (box.exec() != QMessageBox::Yes) return;
 
-    // First remove wallet from node.
-    wallet_model->wallet().remove();
-    // Now release the model.
-    removeAndDeleteWallet(wallet_model);
+    removeWallet(wallet_model);
 }
 
 void WalletController::closeAllWallets(QWidget* parent)
@@ -105,11 +110,8 @@ void WalletController::closeAllWallets(QWidget* parent)
 
     QMutexLocker locker(&m_mutex);
     for (WalletModel* wallet_model : m_wallets) {
-        wallet_model->wallet().remove();
-        Q_EMIT walletRemoved(wallet_model);
-        delete wallet_model;
+        removeWallet(wallet_model);
     }
-    m_wallets.clear();
 }
 
 WalletModel* WalletController::getOrCreateWallet(std::unique_ptr<interfaces::Wallet> wallet)

src/qt/walletcontroller.h

@@ -85,6 +85,9 @@ class WalletController : public QObject
 
     friend class WalletControllerActivity;
     friend class MigrateWalletActivity;
+
+    //! Starts the wallet closure procedure
+    void removeWallet(WalletModel* wallet_model);
 };
 
 class WalletControllerActivity : public QObject