Undefined index: operations in batch_set()

Breaks cron job, and maybe some batches.

Operations should be initialized, like this:

[...]
function taxonomy_orphanage_roundup($progressive = TRUE, $limit = -1) {
  $batch = array(
    'title' => t('Collecting orphans'),
    'file' => drupal_get_path('module', 'taxonomy_orphanage') . '/taxonomy_orphanage.batch.inc',
    'finished' => 'taxonomy_orphanage_batch_finished',
    'operations' => array(),
  );
[...]