Fix crash in horse code

mods/ENTITIES/mobs_mc/horse.lua

@@ -256,6 +256,7 @@ local horse = {
 				local armor = minetest.get_item_group(iname, "horse_armor")
 				self._horse_armor = iname
 				if not minetest.settings:get_bool("creative_mode") then
+					local w = clicker:get_wielded_item()
 					w:take_item()
 					clicker:set_wielded_item(w)
 				end