Chemmaster and chemdispenser UI disables if the machine is not operable (#20101)

Chemmaster and chemdispenser UI disables if the machine is not operable.
Turned a comment into a DMDoc.

Fixes #19825

code/modules/reagents/Chemistry-Machinery.dm

@@ -299,6 +299,11 @@
 		return TRUE
 	return TRUE
 
+/obj/machinery/chem_master/ui_status(mob/user, datum/ui_state/state)
+	if(!operable())
+		return UI_DISABLED
+
+	. = ..()
 
 
 /obj/machinery/chem_master/Topic(href, href_list)

code/modules/reagents/dispenser/dispenser2.dm

@@ -202,6 +202,12 @@
 
 	add_fingerprint(usr)
 
+/obj/machinery/chemical_dispenser/ui_status(mob/user, datum/ui_state/state)
+	if(!operable())
+		return UI_DISABLED
+
+	. = ..()
+
 /obj/machinery/chemical_dispenser/attack_ai(mob/user as mob)
 	if(!ai_can_interact(user))
 		return