in case an invalid drive was configured, now it marks the field
invalid instead of autoselecting the first valid one
this could have lead to users configuring the wrong drive in a
tape-backup-job when they edited one
Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
Reported-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
