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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? -->

<!-- What version of Bitcoin Core are you using, where did you get it (website, self-compiled, etc)? -->

<!-- What type of machine are you observing the error on (OS/CPU and disk type)? -->

<!-- Any extra information that might be useful in the debugging process. -->
<!--- This is normally the contents of a `debug.log` or `config.log` file. Raw text or a link to a pastebin type site are preferred. -->

{
    this->clientModel = _clientModel;
    if(_clientModel)
    {
        
        
        createTrayIconMenu();
        
        updateNetworkState();
        connect(_clientModel, SIGNAL(numConnectionsChanged(int)), this, SLOT(setNumConnections(int)));
        connect(_clientModel, SIGNAL(networkActiveChanged(bool)), this, SLOT(setNetworkActive(bool)));
        modalOverlay->setKnownBestHeight(_clientModel->getHeaderTipHeight(), QDateTime::fromTime_t(_clientModel->getHeaderTipTime()));
        setNumBlocks(m_node.getNumBlocks(), QDateTime::fromTime_t(m_node.getLastBlockTime()), m_node.getVerificationProgress(), false);
        connect(_clientModel, SIGNAL(numBlocksChanged(int,QDateTime,double,bool)), this, SLOT(setNumBlocks(int,QDateTime,double,bool)));
        
        connect(_clientModel, SIGNAL(message(QString,QString,unsigned int)), this, SLOT(message(QString,QString,unsigned int)));
        
        connect(_clientModel, SIGNAL(showProgress(QString,int)), this, SLOT(showProgress(QString,int)));
        rpcConsole->setClientModel(_clientModel);
#ifdef ENABLE_WALLET
        if(walletFrame)
        {
            walletFrame->setClientModel(_clientModel);
        }
#endif 
        unitDisplayControl->setOptionsModel(_clientModel->getOptionsModel());