Fix four routes with auth_desired misimplemented.

PR #374 removed `@auth_required` from a number of routes and changed
those which used their `v` parameters to `v=None` and removed the `v`
parameter from those which didn't internally use it. 1841134b47

PR #392 re-added `@auth_desired` to those routes to ensure the
templates rendered with awareness of the current logged-in user
(matters for search, header bar, etc). 9f042c1aeb

However, 500 errors occurred on /random_post, /random_user, /id/<uid>,
and /u/<username>. Those were the four which had their `v` parameter
removed entirely. This has been re-added, which fixes the bug.

The way to understand auth_required vs auth_desired is that they are
nearly identical, with the sole difference than auth_required
checks if v is None and aborts with 401 if so. This means that
auth_desired routes must handle the v=None case. They are the same in
that they always try to give a `v` kwarg to the decorated function,
which was the root cause of those four routes erroring.

Recommended style: the vast majority of routes which return a rendered
template should be auth_desired, because the top-level templates often
draw extensively from `v` state even when the route handler does not.
When a route is either auth_desired or auth_required, it should have a
`v` parameter, which we typically give as the first positional
parameter.

files/routes/users.py

@@ -753,25 +753,25 @@ def api_is_available(name):
 
 @app.get("/id/<id>")
 @auth_desired
-def user_id(id):
+def user_id(v, id):
 	user = get_account(id)
 	return redirect(user.url)
 		
 @app.get("/u/<username>")
 @auth_desired
-def redditor_moment_redirect(username):
+def redditor_moment_redirect(v, username):
 	return redirect(f"/@{username}")
 
 @app.get("/@<username>/followers")
 @auth_desired
-def followers(username, v=None):
+def followers(v, username):
 	u = get_user(username, v=v)
 	users = g.db.query(User).join(Follow, Follow.target_id == u.id).filter(Follow.user_id == User.id).order_by(Follow.created_utc).all()
 	return render_template("followers.html", v=v, u=u, users=users)
 
 @app.get("/@<username>/following")
 @auth_desired
-def following(username, v=None):
+def following(v, username):
 	u = get_user(username, v=v)
 	users = g.db.query(User).join(Follow, Follow.user_id == u.id).filter(Follow.target_id == User.id).order_by(Follow.created_utc).all()
 	return render_template("following.html", v=v, u=u, users=users)