Reverts change in r13428, project can't be found by identifier (#17959).

git-svn-id: http://svn.redmine.org/redmine/trunk@13429 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/controllers/previews_controller.rb

@@ -45,7 +45,7 @@ class PreviewsController < ApplicationController
 
   def find_project
     project_id = (params[:issue] && params[:issue][:project_id]) || params[:project_id]
-    @project = Project.visible.find(project_id)
+    @project = Project.find(project_id)
   rescue ActiveRecord::RecordNotFound
     render_404
   end