QWindowsFontEngine: Fix warnings about GetGlyphOutline() failures.

tst_qglthreads::painterOnPixmapInThread reports

QWinFontEngine: unable to query transformed glyph metrics...

(Desktop OpenGL only).

Task-number: QTBUG-28264
Change-Id: Ib456905a13a95037ec13dfc4cb828f830076ee89
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>