Project filter cannot be unset/reset

### Describe your issue

I cannot reset the filter of projects. When i first installed the app, i could see all my tasks. I then filtered for a project. If i undo the filter of the project, i see no tasks now.
Also, the filter "All projects" does not help, independent if it is active or not, i cannot see any task.

If i select a project i can see its tasks. But there is no possibility anymore to see all tasks independent of the project. Also, i cannot select a "virtual project" called "no project", where i can see all tasks that do not have a project assigned.

### Steps to reproduce

1. Set up app with task champion
2. See all my tasks
3. Filter for a project
4. Undo the filter
5. Now no tasks are listed anymore

### What was the expected result?

All tasks can be seen when i undo a project filter. But i see no tasks at all then.

### Put here any screenshots or videos (optional)

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### How can we contact you (optional)

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### Would you like to work on this issue?

None

### By submitting this issue, I have confirmed that:

- [x] I have starred the repo ⭐ and watched 👀 it on GitHub and followed the contribution guidelines.

記載されたセットアップ手順とフィルター手順を使ってアプリで問題を再現し、その後、プロジェクトフィルターのリセットと「All projects」の動作を追跡します。プロジェクトフィルターをクリアするとすべてのタスクが表示され、選択可能な「no project」ビューでプロジェクトが割り当てられていないタスクが表示されれば完了です。

索引モデルが issue の本文から書いたものです。