Since by default QStyleOptionProgressBar is initialized with initialize
QStyle::State_Horizontal, the example shouldn't overwrite the state, and
instead OR other states into it. Otherwise, the progressbar will be laid
out vertically.
Pick-to: 6.2 6.3
Fixes: QTBUG-100067
Change-Id: Ibebda48a297af4a621719673033f8199b8bc7984
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>