Fix bugs with loading/reading nonexistent/empty bookmark files
bload to the end of my
config.tako before I had actually run
bwrite, so it errored on the next shell I opened. I then ran
bwrite to make the file and
blist to see what happened, and there was another error because it was an empty JSON object.
The first one might be better as an warning rather than silent failure, but it's going to be a while before I add my first bookmark, and I don't every shell until then to start by yelling at me.