utils: Check if nightMode module is enabled before styling

Fixes #1433. Night mode should not be enabled if the module is disabled.
there's not yet! I was proposing some sort of a lightweight pub/sub system which isn't exactly a tiny task...

I may be wrong about the possible race condition, to be honest (though I think I'm right!), I haven't had the time to go back and read the code more deeply and remember the entire sequence of things.