nuclear_reactor: Add error messages on start failure (#574)

Cedric Haase

2021-01-06 11e43ffe134f6483905b18662a544dec384b231c

 technic/machines/other/coal_alloy_furnace.lua

@@ -77,14 +77,12 @@
   action = function(pos, node, active_object_count, active_object_count_wider)
      local meta = minetest.get_meta(pos)
      local inv    = meta:get_inventory()
		

      if inv:get_size("src") == 1 then -- Old furnace -> convert it
         inv:set_size("src", 2)
         inv:set_stack("src", 2, inv:get_stack("src2", 1))
         inv:set_size("src2", 0)
      end
		
      local recipe = nil

      for i, name in pairs({
            "fuel_totaltime",