Fix when private user following user, private user will not be counted in his own view (#28037) (#28792)

Backport #28037 by @yp05327

Doer: asdasasdasasdasasdasasdasasdasasdasasdas (private user)
Followed: TestUser (public user)

Before:
(From doer's view)

![image](https://github.com/go-gitea/gitea/assets/18380374/9ba16b3b-068c-43c5-a3dd-e3343b5b32f2)
(From followed user's view, can see doer)

![image](https://github.com/go-gitea/gitea/assets/18380374/dfd1b564-d689-4393-b3d3-1e6bf52c94ba)

After:
(From doer's view)

![image](https://github.com/go-gitea/gitea/assets/18380374/1c85c1d1-c9f7-40c8-948c-145f7cae9a04)

Co-authored-by: yp05327 <576951401@qq.com>

models/user/user.go

@@ -1205,6 +1205,8 @@ func isUserVisibleToViewerCond(viewer *User) builder.Cond {
 	return builder.Neq{
 		"`user`.visibility": structs.VisibleTypePrivate,
 	}.Or(
+		// viewer self
+		builder.Eq{"`user`.id": viewer.ID},
 		// viewer's following
 		builder.In("`user`.id",
 			builder.