A semi-opaque ribbon is observed in the main window:

![DeepinScreenshot_bitcoin-qt_20200119212040](https://user-images.githubusercontent.com/32963518/72686984-752bce80-3b02-11ea-8e54-a4d0e6448c1f.png)

![DeepinScreenshot_bitcoin-qt_20200119212253](https://user-images.githubusercontent.com/32963518/72686986-7a891900-3b02-11ea-87b8-cb2a7ff5b791.png)

Tab switching does not remove it. Window moving does not remove it.
It vanishes after window resizing.

**To reproduce**
Run with `-regtest`, generate some blocks (200 in my case), then quit.
Remove `rev00000.dat` file to trigger an error.
Run with `-regtest` and in the dialog "Do you want to rebuild the block database now?" click "OK".

**System information**
Linux Mint 19.3 + Cinnamon 4.4.8

Both versions affected:
- 0.19.0.1 (gitian)
- master + system Qt 5.9.7
{
    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) {