in the GUI, that dark synchronise screen, if "Progress increase per hour" goes negative, then "Estimated time left until synced" says "%n left", not integers, but '%n'. I was expecting a meaningful wording, like "unknown" or "infinity".

## can you reproduce the problem?
I get this behavour by suspending a non-synced node for a few hours and then restoring it.

### What version of bitcoin-core are you using?
0.15.99

## machine:
Atom 330, 2GB RAM, 5400 RPM HDD, GNU/Linux
if (ev->type() == QEvent::ParentAboutToChange) {
        if (parent()) parent()->removeEventFilter(this);
    }
    else if (ev->type() == QEvent::ParentChange) {
        if (parent()) {
            parent()->installEventFilter(this);
            raise();
        }
    }
    return QWidget::event(ev);
}
void ModalOverlay::setKnownBestHeight(int count, const QDateTime& blockDate)
{
    if (count > bestHeaderHeight) {
        bestHeaderHeight = count;
        bestHeaderDate = blockDate;
    }
}
void ModalOverlay::tipUpdate(int count, const QDateTime& blockDate, double nVerificationProgress)