Fix handling of 0x00AD code with symbol fonts (Win/QPA/QPF/fallback)

...by updating HB_Face::isSymbolFont value to make HB know that the font is a symbol font.
U+00AD is a Unicode soft hyphen character, which shouldn't be threated
like a default ignorable (invisible) when 0x00AD occurred in a symbol font.

Change-Id: Idd4760aded644f7f11a1a8d3c03c348abc69a3e4
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>

src/gui/text/qfontengine.cpp

@@ -279,6 +279,7 @@ void *QFontEngine::harfbuzzFace() const
         Q_CHECK_PTR(hbFace);
         if (hbFace->font_for_init != 0)
             hbFace = qHBLoadFace(hbFace);
+        hbFace->isSymbolFont = symbol;
 
         face_ = (void *)hbFace;
         face_destroy_func = hb_freeFace;