Noticed this while reviewing #13529, but it's also in master @ 5ba77df15. On macOS 10.13.6:

```
bitcoin-qt -disablewallet
```

<img width="1354" alt="schermafbeelding 2018-08-01 om 16 03 41" src="https://user-images.githubusercontent.com/10217/43526506-b23264d8-95a4-11e8-81a0-5debcad838ae.png">

The usual progress modal doesn't appear when QT starts, and clicking on the progress bar has no effect. It works fine when there's a wallet present.
{
    if (_optionsModel)
    {
        this->optionsModel = _optionsModel;
        
        connect(_optionsModel, &OptionsModel::displayUnitChanged, this, &UnitDisplayStatusBarControl::updateDisplayUnit);
        
        updateDisplayUnit(_optionsModel->getDisplayUnit());
    }
}
void UnitDisplayStatusBarControl::updateDisplayUnit(int newUnits)
{
    setText(BitcoinUnits::longName(newUnits));
}
void UnitDisplayStatusBarControl::onDisplayUnitsClicked(const QPoint& point)
{
    QPoint globalPos = mapToGlobal(point);
    menu->exec(globalPos);
}
void UnitDisplayStatusBarControl::onMenuSelection(QAction* action)
{
    if (action)
    {
        optionsModel->setDisplayUnit(action->data());
    }
}