http-walker: cleanup more thoroughly

Signed-off-by: Tay Ray Chuan <rctay89@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

http-walker.c

@@ -543,6 +543,23 @@ static int fetch_ref(struct walker *walker, struct ref *ref)
 
 static void cleanup(struct walker *walker)
 {
+	struct walker_data *data = walker->data;
+	struct alt_base *alt, *alt_next;
+
+	if (data) {
+		alt = data->alt;
+		while (alt) {
+			alt_next = alt->next;
+
+			free(alt->base);
+			free(alt);
+
+			alt = alt_next;
+		}
+		free(data);
+		walker->data = NULL;
+	}
+
 	http_cleanup();
 }