nvk/nak/fs: lots of misc changes of varying quality a

The other MR has the start of this, but those commits are fixes for demos, these are more just misc coding done in reaction to crashes but I'm not sure they are 100% correct. I don't think they make things worse, but you may hold stronger opinions on what I'm doing here.

Feel free to cherry-pick anything sane into your tree, or let me know if some of these should be done different.