Should be able query docs with missing paths in index

```bash
127.0.0.1:6379> json.index add inx first $.first
OK
127.0.0.1:6379> json.index add inx llast $.last
OK
127.0.0.1:6379> json.set user1 . '{"first":"Joe"}' INDEX inx
(error) ERR path does not exist
127.0.0.1:6379> json.set user1 . '{"first":"Joe", "last": "Smith"}' INDEX inx
OK
```

