Fix handcuff hud icons appearing on the left and right hand inventory hud slots when handcuffed.

We define the inventory screen objects for hands to be special in that apply overlays to themselves for handcuffed.  By putting that logic on the screen object itself, we allow it to be expanded to other cases besides handcuffs in the future without conflict.

code/_onclick/hud/human.dm

@@ -158,7 +158,8 @@
 		using.alpha = ui_alpha
 		src.adding += using
 
-		inv_box = new /obj/screen/inventory()
+		inv_box = new /obj/screen/inventory/hand()
+		inv_box.hud = src
 		inv_box.name = "r_hand"
 		inv_box.icon = ui_style
 		inv_box.icon_state = "r_hand_inactive"
@@ -173,7 +174,8 @@
 		src.r_hand_hud_object = inv_box
 		src.adding += inv_box
 
-		inv_box = new /obj/screen/inventory()
+		inv_box = new /obj/screen/inventory/hand()
+		inv_box.hud = src
 		inv_box.name = "l_hand"
 		inv_box.icon = ui_style
 		inv_box.icon_state = "l_hand_inactive"

code/_onclick/hud/screen_objects.dm

@@ -12,6 +12,7 @@
 	layer = 20.0
 	unacidable = 1
 	var/obj/master = null	//A reference to the object in the slot. Grabs or items, generally.
+	var/datum/hud/hud = null // A reference to the owner HUD, if any.
 
 /obj/screen/Destroy()
 	master = null
@@ -507,3 +508,20 @@
 				usr.update_inv_l_hand(0)
 				usr.update_inv_r_hand(0)
 	return 1
+
+// Hand slots are special to handle the handcuffs overlay
+/obj/screen/inventory/hand
+	var/image/handcuff_overlay
+
+/obj/screen/inventory/hand/update_icon()
+	..()
+	if(!hud)
+		return
+	if(!handcuff_overlay)
+		var/state = (hud.l_hand_hud_object == src) ? "l_hand_hud_handcuffs" : "r_hand_hud_handcuffs"
+		handcuff_overlay = image("icon"='icons/mob/screen_gen.dmi', "icon_state"=state)
+	overlays.Cut()
+	if(hud.mymob && iscarbon(hud.mymob))
+		var/mob/living/carbon/C = hud.mymob
+		if(C.handcuffed)
+			overlays |= handcuff_overlay

code/modules/mob/living/carbon/human/update_icons.dm

@@ -895,6 +895,11 @@ var/global/list/damage_icon_parts = list()
 		if(hud_used)
 			hud_used.hidden_inventory_update() 	//Updates the screenloc of the items on the 'other' inventory bar
 
+//update whether handcuffs appears on our hud.
+/mob/living/carbon/proc/update_hud_handcuffed()
+	if(hud_used && hud_used.l_hand_hud_object && hud_used.r_hand_hud_object)
+		hud_used.l_hand_hud_object.update_icon()
+		hud_used.r_hand_hud_object.update_icon()
 
 /mob/living/carbon/human/update_inv_handcuffed(var/update_icons=1)
 	if(handcuffed)
@@ -913,6 +918,8 @@ var/global/list/damage_icon_parts = list()
 
 	else
 		overlays_standing[HANDCUFF_LAYER]	= null
+
+	update_hud_handcuffed()
 	if(update_icons)   update_icons()
 
 /mob/living/carbon/human/update_inv_legcuffed(var/update_icons=1)