Skip generation of glyphs for control characters

QFontEngine tries to generate glyphs for ASCII control characters. Those
characters have no glyphs and should therefore not be generated.

Task-number: QTBUG-113848
Change-Id: Ib15a50c642d8bc92bc007ab5522aebc5a7b2993d
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

src/gui/text/qfontengine.cpp

@@ -1863,6 +1863,7 @@ bool QFontEngineMulti::stringToCMap(const QChar *str, int len,
                 && ucs4 != QChar::LineFeed
                 && ucs4 != QChar::CarriageReturn
                 && ucs4 != QChar::ParagraphSeparator
+                && QChar::category(ucs4) != QChar::Other_Control
                 && QChar::category(ucs4) != QChar::Other_PrivateUse) {
             if (!m_fallbackFamiliesQueried)
                 const_cast<QFontEngineMulti *>(this)->ensureFallbackFamiliesQueried();