Function batch_example_finished() uses wrong index of $error_operation

Patch included.

$error_operation in batch_example_finished() is the first element of the remaining $operations in case of error:

    $error_operation = reset($operations);

$operations is an array defined in batch_example_batch_1() and batch_example_batch_2(). A look at $error_operation content from batch 1 if I trigger an error on the very first operation:

array (
  0 => 'batch_example_op_1',
  1 => 
  array (
    0 => '1',
    1 => '(Operation 0)',
  ),
)

And from batch 2:

array (
  0 => 'batch_example_op_2',
  1 => 
  array (
    0 => '(Operation 0)',
  ),
)

In case of error, batch_example_finished() gives the followng message:

    drupal_set_message(
      t('An error occurred while processing @operation with arguments : @args',
        array(
          '@operation' => $error_operation[0],
          '@args' => print_r($error_operation[0], TRUE),
        )
      )
    );

So it will be: "An error occurred while processing batch_example_op_1 with arguments : batch_example_op_1" whereas I believe @args should display a dump of the second element of the array which is Node ID and 'Operation 0' for batch 1 or 'Operation 0' for batch 2.