Issue #19437: Use an identifier for "__name__" string in pickle to improve

Issue #19437: Use an identifier for "__name__" string in pickle to improve
error handling

The following code didn't handle correctly the failure of
PyUnicode_InternFromString("__name__").

if (newobj_str == NULL) {
    newobj_str = PyUnicode_InternFromString("__newobj__");
    name_str = PyUnicode_InternFromString("__name__");
    if (newobj_str == NULL || name_str == NULL)
        return -1;
}