OpenLearn's pending forum posts remain publicly readable by direct ID when moderation mode is enabled

OpenLearn is open-source educational forum software. Prior to commit 844b2a40a69d0c4911580fe501923f0b391313ab, when `safeMode` is enabled, unapproved forum posts are hidden from the public list, but the direct post-read procedure still returns the full post to anyone with the post UUID. Commit 844b2a40a69d0c4911580fe501923f0b391313ab fixes the issue.