Java: `ArrayInit.getInit` has indices < 0 for annotations

### Version
CodeQL CLI version: 2.8.4

### Description of the issue

For array inits as part of annotations CodeQL's `ArrayInit.getInit` erroneously has `index` values < 0 as result.

### Example query
```ql
import java

from ArrayInit init, int index, Expr e
where
init.getInit(index) = e
and index < 0
select init, index, e
```
[Query Console link](https://lgtm.com/query/6322278065984969890/)