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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. -->

{
    if (walletFrame) walletFrame->gotoVerifyMessageTab(addr);
}
#endif 
void BitcoinGUI::updateNetworkState()
{
    int count = clientModel->getNumConnections();
    QString icon;
    switch(count)
    {
    case 0: icon = ":/icons/connect_0"; break;
    case 1: case 2: case 3: icon = ":/icons/connect_1"; break;
    case 4: case 5: case 6: icon = ":/icons/connect_2"; break;
    case 7: case 8: case 9: icon = ":/icons/connect_3"; break;
    default: icon = ":/icons/connect_4"; break;
    }
    QString tooltip;
    if (m_node.getNetworkActive()) {
        tooltip = tr("%n active connection(s) to Bitcoin network", "", count) + QString(".<br>") + tr("Click to disable network activity.");
    } else {
        tooltip = tr("Network activity disabled.") + QString("<br>") + tr("Click to enable network activity again.");
        icon = ":/icons/network_disabled";
    }
    
    tooltip = QString("<nobr>") + tooltip + QString("</nobr>");
    connectionsControl->setToolTip(tooltip);
    connectionsControl->setPixmap(platformStyle->SingleColorIcon(icon).pixmap(STATUSBAR_ICONSIZE,STATUSBAR_ICONSIZE));
}
void BitcoinGUI::setNumConnections(int count)