Warnings (with WP_DEBUG on) of some uninitialised variables

It looks like there are some variables that are not initialised. That’s fine, but when WP_DEBUG is on they produce warnings.

Adding:

```php
$claimreviewedcurrent    = '';
$claimoriginalcurrent    = '';
$claimasssessmentcurrent = '';
```

…to the top of `claim_review_build_claim_box` (in metabox.php) fixes these.