Fix WiiM players not reporting state after a restart (#5893)

# What does this implement/fix?

WiiM players could come up after a Music Assistant restart without
reporting anything: no source, no track, no playback state, until
something else nudged them.

The first poll of a player can land in the short window before its queue
is registered. The WiiM state update asserted the queue was already
there, so it aborted halfway and never published the state it had just
collected. The queue simply not existing yet is a normal startup
condition, so it now falls back to the unknown source and finishes the
update.

Found while going through the nightly logs, where it showed up as an
empty `Error while requesting latest state from player WiiM ...` warning
on every restart.

**Related issue (if applicable):**

- n/a

## Types of changes

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- [x] Bugfix (non-breaking change which fixes an issue) — `bugfix`
- [ ] New feature (non-breaking change which adds functionality) —
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- [ ] Enhancement to an existing feature — `enhancement`
- [ ] New music/player/metadata/plugin provider — `new-provider`
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected) — `breaking-change`
- [ ] Refactor (no behaviour change) — `refactor`
- [ ] Documentation only — `documentation`
- [ ] Maintenance / chore — `maintenance`
- [ ] CI / workflow change — `ci`
- [ ] Dependencies bump — `dependencies`

## Checklist

- [x] The code change is tested and works locally.
- [x] `pre-commit run --all-files` passes.
- [x] `pytest` passes, and tests have been added/updated under `tests/`
where applicable.
- [ ] For changes to shared models, the companion PR in
`music-assistant/models` is linked.
- [ ] For changes affecting the UI, the companion PR in
`music-assistant/frontend` is linked.
- [x] I have read and complied with the project's [AI
Policy](https://github.com/music-assistant/.github/blob/main/AI_POLICY.md)
for any AI-assisted contributions.
- [ ] I have [raised a PR against the documentation
repository](https://github.com/music-assistant/music-assistant.io/blob/main/CONTRIBUTING.md)
targeting the main or beta branch as appropriate.