patch 8.2.2122: Vim9: crash when sourcing vim9script early

Problem:    Vim9: crash when sourcing vim9script early.
Solution:   Use set_option_value() instead of setting p_cpo directly.
            (closes #7441)

src/scriptfile.c

@@ -1491,8 +1491,7 @@ almosttheend:
     si = SCRIPT_ITEM(current_sctx.sc_sid);
     if (si->sn_save_cpo != NULL)
     {
-	free_string_option(p_cpo);
-	p_cpo = si->sn_save_cpo;
+	set_option_value((char_u *)"cpo", 0L, si->sn_save_cpo, 0);
 	si->sn_save_cpo = NULL;
     }
 

src/testdir/test_vim9_script.vim

@@ -2857,6 +2857,17 @@ def Test_invalid_sid()
   delete('Xdidit')
 enddef
 
+def Test_restoring_cpo()
+  writefile(['vim9script', 'set nocp'], 'Xsourced')
+  writefile(['call writefile(["done"], "Xdone")', 'quit!'], 'Xclose')
+  if RunVim([], [], '-u NONE +"set cpo+=a" -S Xsourced -S Xclose')
+    assert_equal(['done'], readfile('Xdone'))
+  endif
+  delete('Xsourced')
+  delete('Xclose')
+enddef
+
+
 def Test_unset_any_variable()
   var lines =<< trim END
     var name: any

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2122,
 /**/
     2121,
 /**/