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.
{
    QDateTime currentDate = QDateTime::currentDateTime();
    
    blockProcessTime.push_front(qMakePair(currentDate.toMSecsSinceEpoch(), nVerificationProgress));
    
    if (blockProcessTime.size() >= 2) {
        double progressDelta = 0;
        double progressPerHour = 0;
        qint64 timeDelta = 0;
        qint64 remainingMSecs = 0;
        double remainingProgress = 1.0 - nVerificationProgress;
        for (int i = 1; i < blockProcessTime.size(); i++) {
            QPair<qint64, double> sample = blockProcessTime[i];
            
            if (sample.first < (currentDate.toMSecsSinceEpoch() - 500 * 1000) || i == blockProcessTime.size() - 1) {
                progressDelta = blockProcessTime[0].second - sample.second;
                timeDelta = blockProcessTime[0].first - sample.first;
                progressPerHour = progressDelta / (double) timeDelta * 1000 * 3600;
                remainingMSecs = (progressDelta > 0) ? remainingProgress / progressDelta * timeDelta : -1;
                break;
            }
        }
        
        ui->progressIncreasePerH->setText(QString::number(progressPerHour * 100, 'f', 2)+"%");
        
        if(remainingMSecs >= 0) {