Health Hud Prosthetics Fix

Adds two lines of code I forgot to port, hopefully should make the prosthetic icons for the HUD be correct now.

code/modules/organs/organ_icon.dm

@@ -122,6 +122,9 @@ var/global/list/limb_icon_cache = list()
 					limb_icon_cache[cache_key] = I
 				mob_icon.Blend(limb_icon_cache[cache_key], ICON_OVERLAY)
 
+	if(model)
+		icon_cache_key += "_model_[model]"
+
 	dir = EAST
 	icon = mob_icon
 	return mob_icon