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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. -->

{
    
    openRPCConsoleAction->setEnabled(true);
    aboutAction->setEnabled(true);
    optionsAction->setEnabled(true);
}
#ifdef ENABLE_WALLET
void BitcoinGUI::incomingTransaction(const QString& date, int unit, const CAmount& amount, const QString& type, const QString& address, const QString& label, const QString& walletName)
{
    
    QString msg = tr("Date: %1\n").arg(date) +
                  tr("Amount: %1\n").arg(BitcoinUnits::formatWithUnit(unit, amount, true));
    if (m_node.getWallets().size() > 1 && !walletName.isEmpty()) {
        msg += tr("Wallet: %1\n").arg(walletName);
    }
    msg += tr("Type: %1\n").arg(type);
    if (!label.isEmpty())
        msg += tr("Label: %1\n").arg(label);
    else if (!address.isEmpty())
        msg += tr("Address: %1\n").arg(address);
    message((amount)<0 ? tr("Sent transaction") : tr("Incoming transaction"),
             msg, CClientUIInterface::MSG_INFORMATION);
}
#endif 
void BitcoinGUI::dragEnterEvent(QDragEnterEvent *event)