Abort on wrong user input

[NicoHood]

You selected the disk with UUID e9155055-f7e6-4975-90c5-3994057b8c64.
The disk is mounted at /media/Raid.

No backups have been performed for 'root' on this disk.
Enter name of directory to store backups, relative to /media/Raid (to be created if not existing): backup/rpi
This will be the initial backup for snapper configuration 'root' to this disk. This could take awhile.
Will backup //.snapshots/8/snapshot to /media/Raid/backup/rpi/root/8//snapshot
Continue with backup [Y/n]? k
Aborting backup for this configuration.

No backups have been performed for 'home' on this disk.
Enter name of directory to store backups, relative to /media/Raid (to be created if not existing): 

If you trype something invalid it should give an error and try again. Too bad "k" is not interpreted as "y" (joke).