SideBarMode: return false in eventFilter if qqw is nullptr
If user presses Alt+Tab in a view that has both QtWidgets and QtQuickWidgets, and
Alt+Tab is not set as a shortcut, systemsettings will crash.
This seems to be because Alt key activates the quick shortcuts in QtWidgets
(the thing that underlines one letter from an element) and the active element
is then not a QtQuickWidget, which is then nullptr, and crashes systemsettings
when nullptr is sent with sendEvent