fsck: fix leak when traversing trees

While fsck_walk/fsck_walk_tree/parse_tree populates "struct tree"
idempotently, it is still up to the fsck_walk caller to call
free_tree_buffer.

Fixes: ad2db403 ("fsck: remove redundant parse_tree() invocation")
Signed-off-by: NEric Wong <e@80x24.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin/fsck.c

@@ -170,7 +170,13 @@ static void mark_object_reachable(struct object *obj)
 
 static int traverse_one_object(struct object *obj)
 {
-	return fsck_walk(obj, obj, &fsck_walk_options);
+	int result = fsck_walk(obj, obj, &fsck_walk_options);
+
+	if (obj->type == OBJ_TREE) {
+		struct tree *tree = (struct tree *)obj;
+		free_tree_buffer(tree);
+	}
+	return result;
 }
 
 static int traverse_reachable(void)