[FIX] website_blog: do not show current blog post as next post

At the bottom of each blog post there is a link to the next blog post
of the blog. If the current blog post is the last, the next blog post
which appears is the first one, which is ok. However, if there is only
one blog post in the blog, when viewing it, the next blog post which
was proposed was the current one (now nothing is proposed as next blog
post anymore).

addons/website_blog/controllers/main.py

@@ -228,8 +228,8 @@ class WebsiteBlog(http.Controller):
         all_post_ids = blog_post_obj.search(cr, uid, [('blog_id', '=', blog.id)], context=context)
         # should always return at least the current post
         current_blog_post_index = all_post_ids.index(blog_post.id)
-        next_post_id = all_post_ids[0 if current_blog_post_index == len(all_post_ids) - 1 \
-                            else current_blog_post_index + 1]
+        nb_posts = len(all_post_ids)
+        next_post_id = all_post_ids[(current_blog_post_index + 1) % nb_posts] if nb_posts > 1 else None
         next_post = next_post_id and blog_post_obj.browse(cr, uid, next_post_id, context=context) or False
 
         values = {