storage: Fix root subvolume identification for Delete action

When nothing is mounted, we don't know the IDs of subvolumes, only
their names. Make the check for whether to include the "Delete" action
also work in that case.

pkg/storaged/btrfs/subvolume.jsx

@@ -299,7 +299,7 @@ export function make_btrfs_subvolume_page(parent, volume, subvol) {
     }
 
     // Don't show deletion for the root subvolume as it can never be deleted.
-    if (subvol.id !== 5)
+    if (subvol.id !== 5 && subvol.pathname !== "/")
         actions.push({
             danger: true,
             title: _("Delete"),