fixed lightning crash

weather/api.lua

@@ -90,9 +90,11 @@ minetest.register_globalstep(function()
 	else
 		if math.random(1, 10000) == 1 then
 			weather.type = "none"
+			if minetest.get_modpath("lightning") then
 				lightning.auto = false
 			end
 		end
+	end
 	local current_downfall = weather_mod.registered_downfalls[weather.type]
 	if current_downfall==nil then return end
 	for _, player in ipairs(minetest.get_connected_players()) do