Fix teleporting into the non-SW 256x256 corner of a megaregion, though currently with a 10 second delay before auto-reteleport to the correct location.

This now does a check for border crossing (required to trigger the teleport) immediately in SP.MakeRootAgent().
If left any later, it looks like the physics scene changes the position and stops the cross happening.
If done any earlier, nothing happens because the cross-code currently requires a PhysicsActor to be in place, thuogh it's probably not necessary for this case.