MDL-32357 Try to fix unread post notification for blog-style forums.

I know that showing unread posts is not 100% blog-style, but I think
it is useful functionality, therefore, I chose to fix it, rather than,
say, disable it completely.

I think this fix will only affect blog-style forums since
forum_print_latest_discussions is only called with mode 'plain' in
three places:
1. Blog-style forums - the case we want to fix,
2. Site news forum, and
3. Social course format.

In all cases, having read tracking work properly seems like the
right thing to do.

mod/forum/lib.php

@@ -5433,7 +5433,8 @@ function forum_print_latest_discussions($course, $forum, $maxdiscussions=-1, $di
 
                 $discussion->forum = $forum->id;
 
-                forum_print_post($discussion, $discussion, $forum, $cm, $course, $ownpost, 0, $link, false);
+                forum_print_post($discussion, $discussion, $forum, $cm, $course, $ownpost, 0, $link, false,
+                        '', null, true, $forumtracked);
             break;
         }
     }