fix some crash related to offhand

mods/HUD/mcl_offhand/init.lua

@@ -56,6 +56,9 @@ end
 
 minetest.register_globalstep(function(dtime)
 	for _, player in pairs(minetest.get_connected_players()) do
+		if not mcl_offhand[player] then
+			goto continue
+		end
 		local itemstack = mcl_offhand.get_offhand(player)
 		local offhand_item = itemstack:get_name()
 		local offhand_hud = mcl_offhand[player].hud
@@ -148,6 +151,7 @@ minetest.register_globalstep(function(dtime)
 				remove_hud(player, index)
 			end
 		end
+		::continue::
 	end
 end)