gui: Consolidate wallet display name to GUIUtil function

Instead of having the code for the wallet display name being copy and
pasted, use a GUIUtil function to get that for us.

src/qt/bitcoingui.cpp

@@ -398,7 +398,7 @@ void BitcoinGUI::createActions()
             m_open_wallet_menu->clear();
             for (const auto& [path, info] : m_wallet_controller->listWalletDir()) {
                 const auto& [loaded, _] = info;
-                QString name = path.empty() ? QString("["+tr("default wallet")+"]") : QString::fromStdString(path);
+                QString name = GUIUtil::WalletDisplayName(path);
                 // An single ampersand in the menu item's text sets a shortcut for this item.
                 // Single & are shown when && is in the string. So replace & with &&.
                 name.replace(QChar('&'), QString("&&"));

src/qt/guiutil.cpp

@@ -1008,4 +1008,13 @@ void ShowModalDialogAsynchronously(QDialog* dialog)
     dialog->show();
 }
 
+QString WalletDisplayName(const QString& name)
+{
+    return name.isEmpty() ? "[" + QObject::tr("default wallet") + "]" : name;
+}
+
+QString WalletDisplayName(const std::string& name)
+{
+    return WalletDisplayName(QString::fromStdString(name));
+}
 } // namespace GUIUtil

src/qt/guiutil.h

@@ -436,6 +436,9 @@ namespace GUIUtil
         return false;
     }
 
+    QString WalletDisplayName(const std::string& name);
+    QString WalletDisplayName(const QString& name);
+
 } // namespace GUIUtil
 
 #endif // BITCOIN_QT_GUIUTIL_H

src/qt/walletcontroller.cpp

@@ -343,7 +343,7 @@ void OpenWalletActivity::finish()
 
 void OpenWalletActivity::open(const std::string& path)
 {
-    QString name = path.empty() ? QString("["+tr("default wallet")+"]") : QString::fromStdString(path);
+    QString name = GUIUtil::WalletDisplayName(path);
 
     showProgressDialog(
         //: Title of window indicating the progress of opening of a wallet.

src/qt/walletmodel.cpp

@@ -594,8 +594,7 @@ QString WalletModel::getWalletName() const
 
 QString WalletModel::getDisplayName() const
 {
-    const QString name = getWalletName();
-    return name.isEmpty() ? "["+tr("default wallet")+"]" : name;
+    return GUIUtil::WalletDisplayName(getWalletName());
 }
 
 bool WalletModel::isMultiwallet() const