Bug: Using docker deploy, Can't delete attachment.

[Sanzro-Lee]

Steps to reproduce the behavior

Using Docker to deploy, with this command docker run -it -p 80:8000 mattermost/focalboard.

1. Get inside a new block
2. Upload something in it
3. Delete it
4. Failed

It's still in place.

[Chirag Jain]

The file uploaded. Then deleted, left its name in directory with size 0kb. And Attachment boxes stays the same.