Merge branch 'mh/packed-refs-do-one-ref-recursion'

Fix a NULL-pointer dereference during nested iterations over
references (for example, when replace references are being used).

* mh/packed-refs-do-one-ref-recursion:
  do_one_ref(): save and restore value of current_ref

refs.c

@@ -634,18 +634,22 @@ struct ref_entry_cb {
 static int do_one_ref(struct ref_entry *entry, void *cb_data)
 {
 	struct ref_entry_cb *data = cb_data;
+	struct ref_entry *old_current_ref;
 	int retval;
+
 	if (prefixcmp(entry->name, data->base))
 		return 0;
 
 	if (!(data->flags & DO_FOR_EACH_INCLUDE_BROKEN) &&
 	      !ref_resolves_to_object(entry))
 		return 0;
 
+	/* Store the old value, in case this is a recursive call: */
+	old_current_ref = current_ref;
 	current_ref = entry;
 	retval = data->fn(entry->name + data->trim, entry->u.value.sha1,
 			  entry->flag, data->cb_data);
-	current_ref = NULL;
+	current_ref = old_current_ref;
 	return retval;
 }