Update the field widths on demand in wxStatusBarGeneric.

This ensures that the value returned from GetFieldRect() is always up to date,
even when this method is called from the user-defined wxEVT_SIZE handler, i.e.
before our own OnSize() could run.

Also remove the now unneeded hack with calling the base class OnSize() from
the statbar sample.

Closes #14268.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71365 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/statbar/statbar.cpp

@@ -947,11 +947,6 @@ void MyStatusBar::OnSize(wxSizeEvent& event)
         return;
 #endif
 
-    // TEMPORARY HACK: TODO find a more general solution
-#ifdef wxStatusBarGeneric
-    wxStatusBar::OnSize(event);
-#endif
-
     wxRect rect;
     if (!GetFieldRect(Field_Checkbox, rect))
     {