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<!-- Describe the issue -->
double click bitcoin icon on the task bar with setting 'minimize to the tray' cause a blank window
<!--- What behavior did you expect? -->
![ezgif com-video-to-gif](https://user-images.githubusercontent.com/11154118/38133010-fad94d80-343f-11e8-8bf4-127100e9c1f4.gif)

<!--- What was the actual behavior (provide screenshots if the issue is GUI-related)? -->

<!--- How reliably can you reproduce the issue, what are the steps to do so? -->

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} else {
        windowTitle += tr("Node");
    }
    windowTitle += " " + networkStyle->getTitleAddText();
#ifndef Q_OS_MAC
    QApplication::setWindowIcon(networkStyle->getTrayAndWindowIcon());
    setWindowIcon(networkStyle->getTrayAndWindowIcon());
#else
    MacDockIconHandler::instance()->setIcon(networkStyle->getAppIcon());
#endif
    setWindowTitle(windowTitle);
#if defined(Q_OS_MAC) && QT_VERSION < 0x050000
    
    
    setUnifiedTitleAndToolBarOnMac(true);
#endif
    rpcConsole = new RPCConsole(node, _platformStyle, 0);
    helpMessageDialog = new HelpMessageDialog(node, this, false);
#ifdef ENABLE_WALLET
    if(enableWallet)
    {
        
        walletFrame = new WalletFrame(_platformStyle, this);
        setCentralWidget(walletFrame);
    } else
#endif 
    {
        /* When compiled without wallet or -disablewallet is provided,
         * the central widget is the rpc console.
         */