Fix rare integer overflow in text shaping

With extreme painter scaling, linearAdvance may be too large to fit in
an unsigned short.

Fixes: QTBUG-91758
Pick-to: 6.1 5.15
Change-Id: I7bbe6e77ec9bcef4aa5259da1d3000ed1a8eb27a
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

src/gui/text/freetype/qfontengine_ft.cpp

@@ -1051,7 +1051,8 @@ QFontEngineFT::Glyph *QFontEngineFT::loadGlyph(QGlyphSet *set, uint glyph,
         info.height = TRUNC(top - bottom);
 
         // If any of the metrics are too large to fit, don't cache them
-        if (areMetricsTooLarge(info))
+        // Also, avoid integer overflow when linearAdvance is to large to fit in a signed short
+        if (areMetricsTooLarge(info) || info.linearAdvance > 0x7FFF)
             return nullptr;
 
         g = new Glyph;