utils: Check if nightMode module is enabled before styling

Fixes #1433. Night mode should not be enabled if the module is disabled.
i feel like the better solution here might be to create a tiny eventing system that modules subscribe to... moduleenabled and moduledisabled events, and night mode module cleanup on moduledisabled deletes localStorage item 'RES_nightMode' ... the whole purpose of storing it up front is to add it as fast as possible to avoid the flash of unstyled content