Fix runtimes related to opt-in checking

[Absolucy]

About The Pull Request

Related:

[2024-07-01 20:07:45.732] runtime error: undefined proc or verb /mob/living/carbon/human/get effective opt in level().
 - 
 - proc name: opt in valid (/datum/objective/proc/opt_in_valid)
 -   source file: monkestation/code/modules/blueshift/optin/objectives.dm,11
 -   usr: null
 -   src: generic objective (/datum/objective/sacrifice)
 -   call stack:
 - generic objective (/datum/objective/sacrifice): opt in valid(Shion Rosenthal (/mob/living/carbon/human))
 - generic objective (/datum/objective/sacrifice): find target(null, null)
 - Cult (/datum/team/cult): setup objectives()
 - /datum/round_event/antagonist/... (/datum/round_event/antagonist/solo/bloodcult): start()
 - /datum/round_event/antagonist/... (/datum/round_event/antagonist/solo/bloodcult): process(2)
 - Events (/datum/controller/subsystem/events): fire(0)
 - Events (/datum/controller/subsystem/events): ignite(0)
 - Master (/datum/controller/master): RunQueue()
 - Master (/datum/controller/master): Loop(2)
 - Master (/datum/controller/master): StartProcessing(0)

Changelog

🆑
fix: Fixed some errors with some objectives, i.e cult sacrifice, trying to find a target.
/:cl: