Minor Changes to DDTeleporter

Made some minor changes to DDTeleporter to get rid of a few warnings.
Also tweaked and commented DDTeleporter.initializeDestination(). There
were inappropriate references to a link's internal variables instead of
using its getters and there was a subtle link overwrite for blacklist
destinations. Without comments, it would probably be unclear that
overwriting that link is safe. This changes are in preparation for
fixing issues with blacklisted destination redirection.
Fixed Flawed Link Redirection

Fixed the way in which we handle redirecting links to blacklisted
dimensions. The previous method always converted links into safe exits.
This lead to strange situations that could be seen as bugs. For
instance, using a dungeon entrance in a root dimension would generate an
exit door and a supporting platform directly above the entrance door.
That also meant that any visited dungeons would be unusable if they were
reset.

We now do different things depending on the location of the link and its
type. If the link is a dungeon link, then its destination is reset to
allow a new dungeon to form. For other link types, if the link is in a
pocket dimension, then it becomes a safe exit link, because it could be
the only way out. If it's in a root dimension, then there are no
reasonable destinations, so the teleport request is cancelled.