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
int est_headers_left = bestHeaderDate.secsTo(QDateTime::currentDateTime()) / Params().GetConsensus().nPowTargetSpacing;
    ui->numberOfBlocksLeft->setText(tr("Unknown. Syncing Headers (%1, %2%)...").arg(bestHeaderHeight).arg(QString::number(100.0 / (bestHeaderHeight + est_headers_left) * bestHeaderHeight, 'f', 1)));
}
void ModalOverlay::toggleVisibility()
{
    showHide(layerIsVisible, true);
    if (!layerIsVisible)
        userClosed = true;
}
void ModalOverlay::showHide(bool hide, bool userRequested)
{
    if ( (layerIsVisible && !hide) || (!layerIsVisible && hide) || (!hide && userClosed && !userRequested))
        return;
    if (!isVisible() && !hide)
        setVisible(true);
    setGeometry(0, hide ? 0 : height(), width(), height());
    QPropertyAnimation* animation = new QPropertyAnimation(this, "pos");
    animation->setDuration(300);
    animation->setStartValue(QPoint(0, hide ? 0 : this->height()));
    animation->setEndValue(QPoint(0, hide ? this->height() : 0));
    animation->setEasingCurve(QEasingCurve::OutQuad);
    animation->start(QAbstractAnimation::DeleteWhenStopped);
    layerIsVisible = !hide;
}
void ModalOverlay::closeClicked()
{
    showHide(true);
    userClosed = true;
}