doors: Fix craftitem not listed in inventory (#1683)

Fixes bug caused by b847888c

mods/doors/init.lua

@@ -254,7 +254,7 @@ function doors.register(name, def)
 	minetest.register_craftitem(":" .. name, {
 		description = def.description,
 		inventory_image = def.inventory_image,
-		groups = def.groups,
+		groups = table.copy(def.groups),
 
 		on_place = function(itemstack, placer, pointed_thing)
 			local pos