Skip empty folders #1716
Description
I use rustic to backup my mailservers and it includes /var/spool/smtpd/queue which may contains a lot of empty folders in structure like: /var/spool/smtpd/queue/XX/YYY where XX is first characters of YYY hash.
"finding used blobs" stage was ~52 minutes on my backup, and as soon as I nuke that empty folders... it goes down to 2 minutes.
Maybe add feature to exclude empty folders from backup at all?