Wraithmonger's Unleash (The player with the fewest Terror tiles claims the highest numbered unclaimed Terror tile and resolves its effect.) is two separate actions. Players do not have to consider whether the player who claims the Terror tile is able to resolve the effect when choosing a valid target for the Unleash.
Example: Wraithmonger Unleashes when no Terror tiles have been claimed. Jian has no cards in hand, but can still choose to be the target of the Unleash and claim Terror tile 7 (Discard a card in hand.). When she attempts to resolve the Terror tile effect, nothing happens.
