Compile master, and run with `src/qt/bitcoin-qt -regtest -nowallet`. As expected, no icon is displayed. Load and unload a wallet. The `HD` icon remains.

On startup:
![on_startup](https://user-images.githubusercontent.com/863730/72410834-711b4c00-37a4-11ea-9a10-bfcf3db7ce68.png)

After a wallet load and unload:
![after_load_unload](https://user-images.githubusercontent.com/863730/72410838-737da600-37a4-11ea-8854-dd13301c0135.png)

{
    if (trayIcon)
    {
        trayIcon->setVisible(!fHideTrayIcon);
    }
}
void BitcoinGUI::showModalOverlay()
{
    if (modalOverlay && (progressBar->isVisible() || modalOverlay->isLayerVisible()))
        modalOverlay->toggleVisibility();
}
static bool ThreadSafeMessageBox(BitcoinGUI* gui, const std::string& message, const std::string& caption, unsigned int style)
{
    bool modal = (style & CClientUIInterface::MODAL);
    
    
    style &= ~CClientUIInterface::SECURE;
    bool ret = false;
    
    bool invoked = QMetaObject::invokeMethod(gui, "message",
                               modal ? GUIUtil::blockingGUIThreadConnection() : Qt::QueuedConnection,
                               Q_ARG(QString, QString::fromStdString(caption)),
                               Q_ARG(QString, QString::fromStdString(message)),
                               Q_ARG(unsigned int, style),
                               Q_ARG(bool*, &ret));
    assert(invoked);
    return ret;
}
void BitcoinGUI::subscribeToCoreSignals()