wff-optimizer: Can/should tool be run recursively?

When run on the same directory, `wff-optimizer` seems to repeatedly resize the same image. Note how `wfs_spring_mindy` is resized twice:

```sh
$ java -jar wff-optimizer/build/libs/wff-optimizer.jar --verbose --source /var/folders/7t/qs57xpxs58j7z20c2g6fryj0006pwv/T/tmp.wLnXqfWWUN | grep spring_mindy
Cropping image wfs_spring_mindy: 400x560 -> 398x338
Scaling image wfs_spring_mindy: 398x338 -> 180x252
$ java -jar wff-optimizer/build/libs/wff-optimizer.jar --verbose --source /var/folders/7t/qs57xpxs58j7z20c2g6fryj0006pwv/T/tmp.wLnXqfWWUN | grep spring_mindy
Scaling image wfs_spring_mindy: 180x252 -> 180x153
$ java -jar wff-optimizer/build/libs/wff-optimizer.jar --verbose --source
```

Is this intentional? How do you know how many passes to apply?