Don't try to check if other reactor chambers are powered if Nuclear Reactor wasn't initialized

Fixes #7

compat/mesecons.lua

@@ -93,6 +93,7 @@ override={
 				if meta:get_int("meseconPowered")==1 then
 					return
 				end
+				if meta:contains("chambers") then
 					local chambers=minetest.deserialize(meta:get_string("chambers"))
 					for _,chamber in ipairs(chambers) do
 						local chamberMeta=minetest.get_meta(chamber)
@@ -100,6 +101,7 @@ override={
 							return
 						end
 					end
+				end
 
 				meta:set_int("enabled",0)
 				meta:set_int("stateChanged",1)