When invoking setWindowFlags with a QStyleSheet and QProxyStyle set, a
repolish is recursivly done creating a second QStyleSheetStyle in
QWidgetPrivate::inheritStyle due to not cleared WA_SetStyle window flag.
This leads to a use-after-free in the then following recursive call to
QStyle::polish. This patch uses the previously create QStyleSheetStyle
in the case that there is already a QStyleSheetStyle for the proxy.
Fixes: QTBUG-125513
Pick-to: 6.7
Change-Id: I841bf68143e893d74ab7373b7a3d3d4ee2bce514
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
(cherry picked from commit 26af5d1854336907d6d7fd6aa1ad060f6d38ce1c)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
899f708c70