cannot restore a specific base backup using its name

[pellcorp]

Using latest master if I try the following:

/usr/local/bin/pghoard_restore get-basebackup --config /var/lib/pghoard/pghoard.json --overwrite --site cluster001 --target-dir /data/postgresql/data/9.5/main/ --restore-to-master --basebackup "cluster001/basebackup/2019-04-01_11-04_0"

I get an error:
FATAL: RestoreError: TypeError: string indices must be integers

This regression was introduced by the MR:

#312

I will raise a MR to fix it