Fix error where energy_collector.lua tries to compare to nil

energy_collector.lua

@@ -95,7 +95,9 @@ local function on_timer(pos, elapsed)
         using_orb = false
     end
 
-    if minetest.get_natural_light(above) >= 14 then
+    local light = minetest.get_natural_light(above)
+
+    if light and light >= 14 then
         if check_for_furnaces(pos, 1, true) then
             -- do nothing, energy is being used for the furnace.
             return true
@@ -306,4 +308,4 @@ exchangeclone.register_energy_collector("exchangeclone:energy_collector_mk5", "E
         {"exchangeclone:energy_collector_mk4", "exchangeclone:energy_collector_mk4", "exchangeclone:energy_collector_mk4"},
         {iron, iron, iron}
     }
-)
+)