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.
ui->expectedTimeLeft->setText(GUIUtil::formatNiceTimeOffset(remainingMSecs / 1000.0));
        } else {
            ui->expectedTimeLeft->setText(QObject::tr("unknown"));
        }
        static const int MAX_SAMPLES = 5000;
        if (blockProcessTime.count() > MAX_SAMPLES) {
            blockProcessTime.remove(MAX_SAMPLES, blockProcessTime.count() - MAX_SAMPLES);
        }
    }
    
    ui->newestBlockDate->setText(blockDate.toString());
    
    ui->percentageProgress->setText(QString::number(nVerificationProgress*100, 'f', 2)+"%");
    ui->progressBar->setValue(nVerificationProgress*100);
    if (!bestHeaderDate.isValid())
        
        return;
    
    
    int estimateNumHeadersLeft = bestHeaderDate.secsTo(currentDate) / Params().GetConsensus().nPowTargetSpacing;
    bool hasBestHeader = bestHeaderHeight >= count;
    
    if (estimateNumHeadersLeft < HEADER_HEIGHT_DELTA_SYNC && hasBestHeader) {
        ui->numberOfBlocksLeft->setText(QString::number(bestHeaderHeight - count));
    } else {
        ui->numberOfBlocksLeft->setText(tr("Unknown. Syncing Headers (%1)...").arg(bestHeaderHeight));
        ui->expectedTimeLeft->setText(tr("Unknown..."));
    }
}
void ModalOverlay::toggleVisibility()