Comparison with uninitialized memory in QTextLayout if a string starts with \t

Conditional jump or move depends on uninitialised value(s)
  in main in /home/user/QTextLineValgrindError/main.cpp:10
  1: saveCurrentGlyph in /home/user/qt/git/qtbase/src/gui/text/qtextlayout.cpp:1693
  2: QTextLine::layout_helper(int) in /home/user/qt/git/qtbase/src/gui/text/qtextlayout.cpp:1933
  3: QTextLine::setLineWidth(double) in /home/user/qt/git/qtbase/src/gui/text/qtextlayout.cpp:1600
  4: qt_format_text(QFont const&, QRectF const&, int, QTextOption const*, QString const&, QRectF*, int, int*, int, QPainter*) in /home/user/qt/git/qtbase/src/gui/painting/qpainter.cpp:7592
  5: qt_format_text(QFont const&, QRectF const&, int, QString const&, QRectF*, int, int*, int, QPainter*) in /home/user/qt/git/qtbase/src/gui/painting/qpainter.cpp:7411
  6: QFontMetrics::boundingRect(QRect const&, int, QString const&, int, int*) const in /home/user/qt/git/qtbase/src/gui/text/qfontmetrics.cpp:868
  7: boundingRect in /home/user/qt/git/qtbase/src/gui/text/qfontmetrics.h:113
  8: QLabelPrivate::sizeForWidth(int) const in /home/user/qt/git/qtbase/src/widgets/widgets/qlabel.cpp:632
  9: QLabel::minimumSizeHint() const in /home/user/qt/git/qtbase/src/widgets/widgets/qlabel.cpp:842
  10: QLabel::sizeHint() const in /home/user/qt/git/qtbase/src/widgets/widgets/qlabel.cpp:825
  11: QWidgetPrivate::adjustedSize() const in /home/user/qt/git/qtbase/src/widgets/kernel/qwidget.cpp:8669
  12: QWidget::adjustSize() in /home/user/qt/git/qtbase/src/widgets/kernel/qwidget.cpp:8729
  13: QWidget::setVisible(bool) in /home/user/qt/git/qtbase/src/widgets/kernel/qwidget.cpp:8329
  14: QWidget::show() in /home/user/qt/git/qtbase/src/widgets/kernel/qwidget.cpp:7893
  15: main in /home/user/QTextLineValgrindError/main.cpp:10