Follow-up to #720 - see commit messages for details.

Currently, it's possible to mislead Rarity by going to an inactive Elemental Storm site while another storm is active on the same map. All NPCs would then be treated as if the storm was enabled at that site, while in reality the pets can't be obtained there. This is unlikely to be a problem in practice and might not be easy to solve, so for now I'll consider it a "known issue" and log it here.

Revisit later, if needed? It's technically a bug, but not really since I chose to accept it (for now) :P