fix(files): catch race condition in FilesWorkspaceHeader init

[skjnldsv]

[skjnldsv]

/backport to stable29

[skjnldsv]

/backport to stable30

[backportbot]

The backport to stable30 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable30
git pull origin stable30

# Create the new backport branch
git checkout -b backport/6733/stable30

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 40cb7cf8

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/6733/stable30

Error: Failed to clone repository: Failed to checkout branches: error: RPC failed; curl 92 HTTP/2 stream 5 was not closed cleanly: CANCEL (err 8)
error: 11118 bytes of body are still expected
fetch-pack: unexpected disconnect while reading sideband packet
fatal: early EOF
fatal: fetch-pack: invalid index-pack output

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Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[skjnldsv]

/backport to stable30