Misc code work.

[galenhuntington]

A few small items:

• There are a number of checks if the playlist is empty, which are unnecessary because it can never be. The process exits on start-up on empty playlist, and anyhow if it didn't the player would crash.
  • This eliminates the last (empty) UI string.
• There was some hacky bounds arithmetic for the folder count, now replaced with length.
• I dropped onPlural since "1/1 dirs" doesn't really read worse than "1/1 dir", and it's an edge case, and anyway it was buggy because it was off by one so only showed the singular with two dirs.
• Other even more minor stuff.