dont abort when (un)ticking labels with no entries shown
[booh] / bin /
drwxr-xr-x   ..
-rwxr-xr-x 196055 booh
-rwxr-xr-x 58411 booh-backend
-rw-r--r-- 59848 booh-classifier
-rw-r--r-- 1021 booh-fix-whitebalance
-rwxr-xr-x 1021 booh-gamma-correction
-rwxr-xr-x 4768 webalbum2booh