If the main window has been minimized to the taskbar (iconified) calling "Show/Hide", "Send" or "Receive" actions from the tray icon menu has no effect: the main window still minimized.

It seems like a Qt bug similar to that old [one](https://bugreports.qt.io/browse/QTBUG-31117).

Tested platform: Linux Mint 19, Qt 5.9.5 / 5.9.6
const std::string BitcoinGUI::DEFAULT_UIPLATFORM =
#if defined(Q_OS_MAC)
        "macosx"
#elif defined(Q_OS_WIN)
        "windows"
#else
        "other"
#endif
        ;
BitcoinGUI::BitcoinGUI(interfaces::Node& node, const PlatformStyle *_platformStyle, const NetworkStyle *networkStyle, QWidget *parent) :
    QMainWindow(parent),
    m_node(node),
    platformStyle(_platformStyle)
{
    QSettings settings;
    if (!restoreGeometry(settings.value("MainWindowGeometry").toByteArray())) {
        
        move(QApplication::desktop()->availableGeometry().center() - frameGeometry().center());
    }
    QString windowTitle = tr(PACKAGE_NAME) + " - ";
#ifdef ENABLE_WALLET
    enableWallet = WalletModel::isWalletEnabled();
#endif 
    if(enableWallet)
    {
        windowTitle += tr("Wallet");
    } else {
        windowTitle += tr("Node");
    }
    windowTitle += " " + networkStyle->getTitleAddText();