patch 8.2.2125: Vim9: leaking memory

Problem:    Vim9: leaking memory.
Solution:   Free the saved 'cpo' value.
diff --git a/src/scriptfile.c b/src/scriptfile.c
index bf4cbc0..aebd98d 100644
--- a/src/scriptfile.c
+++ b/src/scriptfile.c
@@ -1492,7 +1492,7 @@
     if (si->sn_save_cpo != NULL)
     {
 	set_option_value((char_u *)"cpo", 0L, si->sn_save_cpo, 0);
-	si->sn_save_cpo = NULL;
+	CLEAR_POINTER(si->sn_save_cpo);
     }
 
     current_sctx = save_current_sctx;