Notifications shouldn't come through for denied boards

[live627]

Setup

1. Two users: admin and global moderator
2. The preinstalled board with default permissions

Recreate

1. Create a membergroup
2. Set that membergroup to deny as board
3. Add that group to a member
4. That member should receive alerts from a topic in that board
5. Admin replies to that topic

And then the alert comes even though the user is in a group that denies access. If I understand denied access, it should override any group that granted access.