Gitea profile feed disclosure bypassing user visibility

Requesting a user or organization profile page (`GET /{username}`) with an `Accept: application/rss+xml` or `Accept: application/atom+xml` header returned the owner's activity feed without the visibility check that the profile page and the `.rss` and `.atom` routes apply. Anonymous users, restricted users and non-members could confirm the existence of limited or private users and private organizations and read their profile details and public activity, also when `[other] ENABLE_FEED` was disabled. Activity in private repositories was not included.