Division by zero in QTextEngine::positionInLigature

    if (clusterLength) {
        const QGlyphLayout &glyphs = shapedGlyphs(si);
        QFixed glyphWidth = glyphs.effectiveAdvance(glyph_pos);
        // the approximate width of each individual element of the ligature
        QFixed perItemWidth = glyphWidth / clusterLength;
        QFixed left = x > edge ? edge : edge - glyphWidth;
        int n = ((x - left) / perItemWidth).floor().toInt();
        QFixed dist = x - left - n * perItemWidth;
        int closestItem = dist > (perItemWidth / 2) ? n + 1 : n;
        if (cursorOnCharacter && closestItem > 0)
            closestItem--;
        int pos = si->position + clusterStart + closestItem;
        // Jump to the next charStop
        while (!attrs[pos].charStop && pos < end)
            pos++;
        return pos;
    }