Handle null DCL name ownership records

## Description

Production logs for `worlds-content-server-blue` show a recurring unhandled promise rejection in the owner update cron:

```text
null.toLowerCase
/app/dist/adapters/update-owner-job.js:42 -> src/adapters/update-owner-job.ts:42
```

The issue appears to happen while `update-owner-job` calls `nameOwnership.findOwners()` to process DCL name ownership from the marketplace subgraph. Some returned NFT/name field can be `null`, and the code calls `.toLowerCase()` without guarding the value.

## Expected Behavior

The owner update cron should tolerate malformed or incomplete subgraph records and skip records that cannot be mapped, without producing unhandled promise rejections.

## Context

Observed in PRD CloudWatch logs over the last 48h. The error recurs approximately every 12 hours, matching the owner update cron schedule.

Reported by Lautaro Petaccio
Requested by Lautaro Petaccio (<@U025WCHLMN3>)