Error 500 when trying to open LFS files stored on S3 in the WebUI

[x-8523]

• Gitea version (or commit ref): Gitea version 1.14.0+dev-539-ga21adf92e built with GNU Make 4.1, go1.15.6 : bindata, sqlite, sqlite_unlock_notify
• Git version: Git Version: 2.29.2, Wire Protocol Version 2 Enabled
• Operating system: CentOS Linux release 7.9.2009 (Core)

We downloaded gitea from your website.
Gitea is run through systemd.

• Database (use [x]):
  • PostgreSQL
  • MySQL
  • MSSQL
  • SQLite
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL)
  • No (we didn't try; the issue only appears when storing LFS files on S3)
• Log gist:

routers/repo/lfs.go:277:LFSFileGet() [E] Data: EOF

Description

We enabled LFS and configured it to use the minio (S3) backend.
Uploading and downloading LFS files using git(1) works just fine, but we cannot preview LFS files in the WebUI: gitea returns an error 500 every time. This issue didn't appear when we tried using the filesystem backend.
So it looks like the WebUI is unable to display LFS files when they are hosted on S3. We suspect it has something to do with having to download the file first.

We originally tried with Gitea version 1.13.1 built with GNU Make 4.1, go1.15.6 : bindata, sqlite, sqlite_unlock_notify, but updated to 1.14.0+dev-539-ga21adf92e to confirm the issue was still present on master.

Screenshots

It is a generic error 500, but we can provide a screenshot if needed.