Fix lightning

Fixes #632
Error caused by buffer overflow in scenery load. I've added in some extra resets of lightning to prevent any small issues.

Note #635 is not related to this and it requires its own fix.
Screen flags is a bit different with how it uses flags.
Please change to SCREEN_FLAGS_TITLE_DEMO, that is what it should be. Although technically it should probably be != SCREEN_FLAGS_PLAYING.

If you just look at the code, it wouldn't make sense for it to not play rain or thunder if you are "playing".