[Borgbackup] borg delete failure with stack trace

[jonikelee at gmail.com]

I saw posted in github issue #4796 a request that I try 'borg
delete --cache-only borgrepo'.

I just tried that, then retried 'borg create --exclude-if-present
'.nobackup' --stats borgrepo::fourth /home/me'.  The result was the
same stack trace as previously, with the FileNotFoundError about
/<...>/borgrepo/data/0/7