Do not choke on users that weren't cleaned up yet

(cherry picked from commit 92e6c8f3ff)

Backports: https://github.com/opencloud-eu/opencloud/pull/2944
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Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f