Fix 404 if Group guest visit empty group page

app/controllers/groups_controller.rb

@@ -110,7 +110,7 @@ class GroupsController < ApplicationController
   # Dont allow unauthorized access to group
   def authorize_read_group!
-    unless projects.present? or can?(current_user, :manage_group, @group)
+    unless projects.present? or can?(current_user, :read_group, @group)
       return render_404
     end
   end

app/models/ability.rb

@@ -135,6 +135,10 @@ class Ability
     def group_abilities user, group
       rules = []
+      if group.users.include?(user)
+        rules << :read_group
+      end
+
       # Only group owner and administrators can manage group
       if group.owners.include?(user) || user.admin?
         rules << [