QML TextEdit crash with long text

// Scan in logClusters[from..to-1] for glyph_pos
int QTextEngine::getClusterLength(unsigned short *logClusters,
                                  const HB_CharAttributes *attributes,
                                  int from, int to, int glyph_pos, int *start)
{
    int clusterLength = 0;
    for (int i = from; i < to; i++) {
        if (logClusters[i] == glyph_pos && attributes[i].charStop) {  // <-- crashes as logClusters is an invalid pointer
            if (*start < 0)
                *start = i;
            clusterLength++;
        }
        else if (clusterLength)
            break;
    }
    return clusterLength;
}