Qt Font Discovery resolves to a QFont which QFontEngine can not handle

PROBLEM:

As reported in FreeCAD: FreeCAD/issues/10514:

Qt Font Discovery on both Qt-5 and Qt-6:

https://doc.qt.io/qt-5/qfont.html#fontmatching

https://doc.qt.io/qt-6/qfont.html#fontmatching

will resolve to a "bad font", that is, the QFont which QFontEngine can not handle:

https://code.qt.io/cgit/qt/qtbase.git/tree/src/gui/text/qfontengine.cpp?h=5.15#n652

https://code.qt.io/cgit/qt/qtbase.git/tree/src/gui/text/qfontengine.cpp?h=6.6.1#n564

This leads to multiple failures in multiple places in Qt library during the application lifetime.

SOLUTION:

Qt Font Discovery should filter out QFontEngine "bad fonts" from resolution process results.