fix crash in battery mod (missing meta check)

Vanessa Ezekowitz

2017-04-11 3f8478086db8720c0f4b5066779a55a2d0271260

 technic/machines/register/battery_box.lua

@@ -253,6 +253,7 @@
         after_place_node = data.tube and pipeworks.after_place,
         after_dig_node = technic.machine_after_dig_node,
         on_receive_fields = function(pos, formname, fields, sender)
            local meta = minetest.get_meta(pos)
            local nodename = minetest.get_node(pos).name
            if fields.edit_channel then
               minetest.show_formspec(sender:get_player_name(),