Refactors occupant to use setter (#54373)

This is to make it easier to attach a signal to the setting of the occupant.

code/game/objects/items/implants/implantchair.dm

@@ -37,12 +37,13 @@
 
 /obj/machinery/implantchair/ui_data()
 	var/list/data = list()
-	data["occupied"] = occupant ? 1 : 0
+	var/mob/living/mob_occupant = occupant
+
+	data["occupied"] = mob_occupant ? 1 : 0
 	data["open"] = state_open
 
 	data["occupant"] = list()
-	if(occupant)
-		var/mob/living/mob_occupant = occupant
+	if(mob_occupant)
 		data["occupant"]["name"] = mob_occupant.name
 		data["occupant"]["stat"] = mob_occupant.stat
 
@@ -65,7 +66,7 @@
 				open_machine()
 			. = TRUE
 		if("implant")
-			implant(occupant,usr)
+			implant(occupant, usr)
 			. = TRUE
 
 /obj/machinery/implantchair/proc/implant(mob/living/M,mob/user)