Fix deleting pending editor controls if wxPG is destructed from within its own event handler.

If wxPG dtor is invoked from within event handler then deleting its pending editor controls should be delegated to the global idle event handler.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78031 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775