fixes small zparallax bug (#67244)
fixes small zparallax bug (#67244)

fixes an issue where if you attempted to regain control of your initial body after possessing another body it caused a stack trace due to MOB_LOGIN signal not being unregistered

(This was tsu's fault, introduced in a9d8be4d16c90bc4c219318ffba8140e815c6f12)
tgstation/tgstation,tgstation/tgstation,CPTANT/-tg-station,MicroWorldwide/SS13-TG-station,CPTANT/-tg-station,CPTANT/-tg-station,ShizCalev/tgstation,MicroWorldwide/SS13-TG-station,tgstation/-tg-station,tgstation/tgstation,Bawhoppen/-tg-station,MicroWorldwide/SS13-TG-station,MicroWorldwide/SS13-TG-station,ShizCalev/tgstation,MicroWorldwide/SS13-TG-station,ShizCalev/tgstation,tgstation/tgstation,MicroWorldwide/SS13-TG-station,tgstation/tgstation,MicroWorldwide/SS13-TG-station,CPTANT/-tg-station,tgstation/tgstation,Bawhoppen/-tg-station,ShizCalev/tgstation,CPTANT/-tg-station,Bawhoppen/-tg-station,ShizCalev/tgstation,ShizCalev/tgstation,CPTANT/-tg-station,Bawhoppen/-tg-station,MicroWorldwide/SS13-TG-station,Bawhoppen/-tg-station,ShizCalev/tgstation,CPTANT/-tg-station,Bawhoppen/-tg-station,tgstation/-tg-station,CPTANT/-tg-station,Bawhoppen/-tg-station,tgstation/tgstation,tgstation/-tg-station,tgstation/-tg-station,Bawhoppen/-tg-station,tgstation/tgstation,ShizCalev/tgstation