Fix broken conditional check that identifies whether content is cached in order to clean it.

.sandstorm/launcher.sh

@@ -65,8 +65,7 @@ function cleanup()
         -mindepth 1 -type d -empty -delete
 
     # remove files older than ${retention_days} days from the cache
-    if [ -e "${data_path}"/cache/?/ ]
-    then
+    if [ ! -z "$(ls -A $data_path/cache)" ]; then
         find "${data_path}"/cache/?/ -type f -mtime +${retention_days} -delete
     fi
 }