Prevent renaming already renamed wxPG property waiting for deferred deletion.

Name of the property to be deleted with delay is changed to the some meaningless name in order to avoid conflict with other active properties.
It is enough to do this only once.

See #16617

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78029 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775