tree-wide: is_ok/is_err()

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

src/api2/tape/backup.rs

@@ -642,7 +642,7 @@ pub fn backup_snapshot(
         }
     }
 
-    if let Err(_) = reader_thread.join() {
+    if reader_thread.join().is_err() {
         bail!("chunk reader thread failed");
     }