Duplicates images when creating previews

[prolibre]

I'm opening a new ticket... the developers are going to curse me :-)

I've noticed some duplication when creating preview images. In fact, I just had an example in front of me.
Someone has rated a book and I have two successive tasks:
bookwyrm.preview_images.generate_edition_preview_image_task

with the same args (44461,) but with two different UIDDs.
As a result, I have two images in my images/previews/covers folder

40599-b5dac480-45c0-417a-a29d-1f05914d97db.jpg
and
40599-b5dac480-45c0-417a-a29d-1f05914d97db_YeAgDq0.jpg

Of course, only one is attached to the book in question.

It's not an exceptional bug because I have lots of duplicate images with slightly different names.

These duplicate images are in addition to the bug concerning the non-deletion of cover images #2996 :-(
Just so you know, I clean up regularly with bash and delete a lot of useless images (I don't know python and unfortunately I can't contribute to Bookwyrm because of this).