fix #3060:: improve get_owner error handling

log invalid owners to system log, and continue with next group just as
if permission checks fail for the following operations:
- verify store with limited permissions
- list store groups
- list store snapshots

all other call sites either handle it correctly already (sync/pull), or
operate on a single group/snapshot and can bubble up the error.

Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>

src/backup/verify.rs

@@ -516,7 +516,12 @@ pub fn verify_all_backups(
                             && !owner.is_token()
                             && group_owner.user() == owner.user())
                 },
-                Err(_) => false,
+                Err(err) => {
+                    // intentionally not in task log
+                    // the task user might not be allowed to see this group!
+                    println!("Failed to get owner of group '{}' - {}", group, err);
+                    false
+                },
             }
         } else {
             true