QTextEngine: Crash handling QTextDocument with BIDI characters

Starting at line 2791:
 QFixed glyphWidth = glyphs.effectiveAdvance(glyph_pos);              // <---- glyphs.effectiveAdvance returns 0
 // the approximate width of each individual element of the ligature
 QFixed perItemWidth = glyphWidth / clusterLength;                    // <----- perItemWidth is then 0 too
 QFixed left = x > edge ? edge : edge - glyphWidth;
 int n = ((x - left) / perItemWidth).floor().toInt();                 // Division by 0 resulting QFixed assign high value
 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)                           // Crash accessing attrs[] with high pos
      pos++;

 while( pos < end && !attrs[pos].charStop )
      pos++;