Fix decorated text in extra-selections

Change ddef89b323 broke decorations
set using setExtraSelections(), because these decorations are
drawn with a second drawTextItem() call where numGlyphs is
set to 0. When the drawTextDecoration() call was moved into
the branches for multi/no-multi font engines, the call for
the cut-off when numGlyphs == 0 was unintentionally removed.

Task-number: QTBUG-54626
Change-Id: Ieb9fc23099a9d7daf87cc364d3fc9da128ec516d
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/gui/painting/qpainter.cpp

@@ -6439,7 +6439,8 @@ void QPainterPrivate::drawTextItem(const QPointF &p, const QTextItem &_ti, QText
         updateState(state);
 
     if (!ti.glyphs.numGlyphs) {
-        // nothing to do
+        drawTextItemDecoration(q, p, ti.fontEngine, textEngine, ti.underlineStyle,
+            ti.flags, ti.width.toReal(), ti.charFormat);
     } else if (ti.fontEngine->type() == QFontEngine::Multi) {
         QFontEngineMulti *multi = static_cast<QFontEngineMulti *>(ti.fontEngine);