patch 8.2.1127: Vim9: getting a dict member may not work

Problem:    Vim9: getting a dict member may not work.
Solution:   Clear the dict only after copying the item. (closes #6390)
diff --git a/src/vim9execute.c b/src/vim9execute.c
index b4acb35..bcacaab 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -2188,6 +2188,7 @@
 		{
 		    dict_T	*dict;
 		    dictitem_T	*di;
+		    typval_T	temp_tv;
 
 		    tv = STACK_TV_BOT(-1);
 		    if (tv->v_type != VAR_DICT || tv->vval.v_dict == NULL)
@@ -2203,8 +2204,11 @@
 			semsg(_(e_dictkey), iptr->isn_arg.string);
 			goto failed;
 		    }
-		    clear_tv(tv);
+		    // Clear the dict after getting the item, to avoid that it
+		    // make the item invalid.
+		    temp_tv = *tv;
 		    copy_tv(&di->di_tv, tv);
+		    clear_tv(&temp_tv);
 		}
 		break;