twitter_api/remote_follow: allow leading @ in nicknames

And never attempt to fetch nicknames as URLs

lib/pleroma/web/twitter_api/controllers/remote_follow_controller.ex

@@ -29,9 +29,16 @@ defmodule Pleroma.Web.TwitterAPI.RemoteFollowController do
   # GET /ostatus_subscribe
   #
   def follow(%{assigns: %{user: user}} = conn, %{"acct" => acct}) do
-    case is_status?(acct) do
-      true -> follow_status(conn, user, acct)
-      _ -> follow_account(conn, user, acct)
+    cond do
+      String.starts_with?(acct, "@") ->
+        follow_account(conn, user, String.slice(acct, 1..-1//1))
+
+      String.starts_with?(acct, "http://") ||
+          (String.starts_with?(acct, "https://") && is_status?(acct)) ->
+        follow_status(conn, user, acct)
+
+      true ->
+        follow_account(conn, user, acct)
     end
   end