How to reproduce:

- Install document in v17.0 with demo data
- In the kanban view, upload an image in Marketing folder
- The image is displayed as thumbnail in the kanban card
- Upgrade to saas-17.4
- Open Document and go to marketing folder

There is no thumbnail for the uploaded image.

In v17, _compute_thumbnail_status write a False status when the thumbnail is updated because when it is trigerred the attachment is not yet created. So the thumbnail is present but its status is incorrect. It works in v17 because the status is ignored by the view for images but in v17.4, the status is not ignored and the thumbnail is then not displayed.

This temporary fix allows already migrated user to see thumbnail (as the view could not be modified in stable without an upgrade).

We force the status of the thumbnail to "present" when there is no status for a thumbnail of an image which should cover the case where the status was not updated after the thumbnail creation. We have chosen this solution as the thumbnail will be updated in the upgrade and the URL returns anyway a placeholder image if the image is not present.

We modify some tests to check that the patch is applied. As the kanban test  data includes an image with a False status, the patch turns automatically the status to "present". So instead of having the generic mime type thumbnail, we get the actual thumbnail of the image. We change the assertions accordingly to test the new behavior and test the generic mime type thumbnail in the pdf case of the test "document inspector: document preview".

Task-4642866