gh-98978: Fix Py_SetPythonHome(NULL) (GH-99066)

Fix use-after-free in Py_SetPythonHome(NULL), Py_SetProgramName(NULL)
and _Py_SetProgramFullPath(NULL) function calls.

Issue reported by Benedikt Reinartz.
(cherry picked from commit b07f546ea3a574bc3016fb023c157c65a47f4849)

Co-authored-by: Victor Stinner <vstinner@python.org>