Fixes multiple embryos in single host

Added checks so you can’t have multiple embryos in a single host.
Checks are included in both facehugger.dm and alien_embryo.dm, because
there might be ways to implant embryos without facehuggers in the
future, but we also want to avoid creating and instantly deleting
objects.
Also changes chest augmentation surgery to remove any embryos. Before
you could remove the whole chest without finding the embryo inside.

code/modules/mob/living/carbon/alien/special/alien_embryo.dm

@@ -14,8 +14,10 @@ var/const/ALIEN_AFK_BRACKET = 450 // 45 seconds
 
 	if(istype(loc, /mob/living))
 		affected_mob = loc
-		if(affected_mob.getlimb(/obj/item/organ/limb/robot/chest)) //If our Victim is augmented in the chest, No Babby - RR
+		if(affected_mob.getlimb(/obj/item/organ/limb/robot/chest) | affected_mob.status_flags & XENO_HOST) //If our Victim is augmented in the chest, No Babby - RR
+			Del(src)
 			return
+		affected_mob.status_flags |= XENO_HOST
 		processing_objects.Add(src)
 		spawn(0)
 			AddInfectionImages(affected_mob)

code/modules/mob/living/carbon/alien/special/facehugger.dm

@@ -161,14 +161,15 @@ var/const/MAX_ACTIVE_TIME = 400
 
 	if(!sterile)
 		//target.contract_disease(new /datum/disease/alien_embryo(0)) //so infection chance is same as virus infection chance
-		new /obj/item/alien_embryo(target)
-		target.status_flags |= XENO_HOST
-
 		target.visible_message("\red \b [src] falls limp after violating [target]'s face!")
 
 		Die()
 		icon_state = "[initial(icon_state)]_impregnated"
 
+		if(!target.getlimb(/obj/item/organ/limb/robot/chest) && !(target.status_flags & XENO_HOST))
+			new /obj/item/alien_embryo(target)
+
+
 		if(iscorgi(target))
 			var/mob/living/simple_animal/corgi/C = target
 			src.loc = get_turf(C)