Users don't receive default notifications if another setting is set.

Problem 1: All newly signed up users who subscribe to a topic / forum do not receive board notifications.

How to replicate:

1. Sign up as any new user
2. Subscribe to a thread / forum
3. You will not receive board notifications upon a new post / topic.

Expected behaviour:

The default preference is to receive board notifications, and it's checked in the UCP, so they should receive a board notification upon the new post / topic.

Problem 2: Subscribing by email breaks subscribing by board notifications.

How to replicate:

1. Sign up as any new user
2. Go to notification options
3. Check "subscribed by email" for "quote" and hit submit.
4. You will not receive board notifications for "quote" anymore, even though the preference is checked.

Expected behaviour:

The default preference is to receive board notifications, and it's checked in the UCP, so they should receive a board notification when quoted.

Cause:

• The "default" notification option only works if there are NO rows in phpbb_user_notifications for that "item_type".
• The "default" preference for board notifications is to receive them. However, the default stops working when there is a row for "notification.method.email" and no row for "notification.method.board".