keyringer backend: handle 'Nothing matches' output, keyringer doesn't fail properly

src/ldaptool/search/config.py

@@ -121,7 +121,10 @@ class Keyringer(PasswordManager):
             check=True,
             encoding="utf-8",
         )
-        return result.stdout.strip()
+        password = result.stdout.strip()
+        if "Nothing matches , try again." in password:
+            raise SystemExit(f"No password stored for {secretname}")
+        return password
 
 
 @dataclasses.dataclass