battery_box.lua: Make "srcstack" local (#525)

fgrosswig

2020-01-06 e90b28895cc28daf1a2e4fb772bd191400cf9e62

 technic/tools/sonic_screwdriver.lua

@@ -86,7 +86,7 @@
      return itemstack
   end,
})
 

minetest.register_craft({
   output = "technic:sonic_screwdriver",
   recipe = {