The parent of wxRibbonPanel is not always a wxRibbonPage, it can also be the
containing wxFrame itself if the panel is a temporarily expanded one created
when the user clicks a panel reduced to a button. So don't rely on the cast of
the parent to wxRibbonPage to always work. This is ugly but at least avoids a
crash.
Closes#16215.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76437 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775