- Backport of #2134
- It's possible that `canSoftDeleteContentHistory` is called without
`ctx.Doer` being set, such as an anonymous user requesting the
`/content-history/detail` endpoint.
- Add a simple condition to always set to `canSoftDelete` to false if an
anonymous user is requesting this, this avoids a panic in the code that
assumes `ctx.Doer` is set.
- Added integration testing.
(cherry picked from commit 0b5db0dcc6)
