Adding a main menu item for a board that is hidden from regular view breaks the unread counter

1. Create a category and check “Hide forum on the forum list”.
2. Create a forum in that category.
3. Create a new main menu item pointing to the category.
4. Create a thread in the forum created in step 2.
5. Log-In with a user that did not yet read the thread.
6. Notice that the main menu item does not show that one thread is not yet read.
7. Uncheck “Hide forum on the forum list”.
8. Notice that the main menu item now shows that one thread is not yet read.

In addition: The “Forum” main menu item probably should not count threads in boards that are below a board that is hidden in the forum list. Only when a hidden forum is directly linked it (and it’s children) should be included in the counters.