Romerol tumors in living non-zombies don't delete on death (#79945)

## About The Pull Request

Romerol tumors have been broken for over a month because Melbert made
them delete on host death, without realizing that people without
`TRAIT_NODEATH` can have them (namely, non-zombies). This simply puts
the self-deletion behind an `iszombie` check.

## Why It's Good For The Game

This was an oversight that went under the radar until I saw someone get
denied a zombie outbreak because of it.

## Changelog

🆑
fix: People exposed to romerol while alive will once again revive as
zombies on death.
/🆑

Co-authored-by: Mothblocks <35135081+Mothblocks@users.noreply.github.com>

code/modules/zombie/organs.dm

@@ -47,7 +47,8 @@
 
 /obj/item/organ/internal/zombie_infection/proc/organ_owner_died(mob/living/carbon/source, gibbed)
 	SIGNAL_HANDLER
-	qdel(src) // Congrats you somehow died so hard you stopped being a zombie
+	if(iszombie(source))
+		qdel(src) // Congrats you somehow died so hard you stopped being a zombie
 
 /obj/item/organ/internal/zombie_infection/on_find(mob/living/finder)
 	to_chat(finder, span_warning("Inside the head is a disgusting black \