dwrite: Fix crash when loading unsupported font in QRawFont

When we tried loading an unsupported font, there was an unchecked
nullptr which caused crashes later.

This is a hotfix for 6.6 and older versions, as in Qt 6.7 it is
already part of 500be123f4fbb60593fe25d5fe70fbc62445e8aa.

Pick-to: 6.5 6.2 5.15
Fixes: QTBUG-123454
Change-Id: I954a39b5e26714b1cc197d2870e9caef87b0423e
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

src/gui/text/windows/qwindowsfontdatabasebase.cpp

@@ -761,6 +761,9 @@ QFontEngine *QWindowsFontDatabaseBase::fontEngine(const QByteArray &fontData, qr
         return nullptr;
 
     IDWriteFontFace *directWriteFontFace = createDirectWriteFace(fontData);
+    if (directWriteFontFace == nullptr)
+        return nullptr;
+
     fontEngine = new QWindowsFontEngineDirectWrite(directWriteFontFace,
                                                    pixelSize,
                                                    fontEngineData);