I can reproduce an issue with master; v0.17.1rc1 works fine.

Steps to reproduce:
- `bitcoin-qt -regtest`
- open Console window
- repeat `generatetoaddress 1 AN_ADDRESS` some times until crash

Crash occurs both on wayland and x11.

[debug.log](https://github.com/bitcoin/bitcoin/files/2690776/debug.log)

[wallets.zip](https://github.com/bitcoin/bitcoin/files/2690781/wallets.zip)
{
#ifndef Q_OS_MAC 
    if(clientModel && clientModel->getOptionsModel())
    {
        if(!clientModel->getOptionsModel()->getMinimizeOnClose())
        {
            
            rpcConsole->close();
            QApplication::quit();
        }
        else
        {
            QMainWindow::showMinimized();
            event->ignore();
        }
    }
#else
    QMainWindow::closeEvent(event);
#endif
}
void BitcoinGUI::showEvent(QShowEvent *event)