ui: tape: fix restore datastore mapping parameter construction

ui: tape: fix restore datastore mapping parameter construction

We recently took into account the selected datastore when restoring
from tape, but the snapshot grids value may not only be a single
datastore, it can also be a list of snapshots, datastores or 'all'.

Handle these cases and extract the source datastore correctly.

This fixes tape restoration when not a whole datastore is selected.

Reported in the forum:
https://forum.proxmox.com/threads/restore-from-lto-parameter-verification-errors-store.128445

Fixes: df881ed0 ("ui: tape: fix restoring a single datastore")
Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>