[FIX] website_blog: fix pager when existing filters in url

Go to a URL such as `/blog/our-news-1?date_begin=2015-01-01`
Now click on page 2.

Without this patch you will go to `/blog/our-news-1?date_begin=2015-01-01/page/2`.
With this patch, you will go to `/blog/our-news-1/page/2?date_begin=2015-01-01`.

This commit closes #13206

addons/website_blog/controllers/main.py

@@ -127,10 +127,11 @@ class WebsiteBlog(http.Controller):
         blog_posts = blog_post_obj.browse(cr, uid, blog_post_ids, context=context)
 
         pager = request.website.pager(
-            url=blog_url(),
+            url=request.httprequest.path,
             total=len(blog_posts),
             page=page,
             step=self._blog_post_per_page,
+            url_args=opt,
         )
         pager_begin = (page - 1) * self._blog_post_per_page
         pager_end = page * self._blog_post_per_page