#616 "Incremental backup" is selectable for image backup

[Matthias Böhm]

When I start a backup for a backup with "image" storage mode, I can select "Incremental backup", although a backup in "image" storage mode is always a full backup (see attached image).

[Matthias Böhm]

Sorry, the text is a little bit incomprehensible. Here an improved version:

When I start a backup with "image" storage mode, I can select "Incremental backup", although a backup in "image" storage mode is always a full backup (see attached image).