Can't assume the block module is on

Line 261 of print.pages.inc calls block_get_blocks_by_region() but I work on many sites that don't ever have the block module on because they only use panels for layout.

<?php
  switch (variable_get('print_footer_options', PRINT_FOOTER_OPTIONS_DEFAULT)) {
    case 1: // theme's
      $footer_blocks = block_get_blocks_by_region('footer');
      $footer = variable_get('site_footer', FALSE) . "\n" . drupal_render($footer_blocks);
      break;
    case 2: // user-specifed
      $footer = variable_get('print_footer_user', PRINT_FOOTER_USER_DEFAULT);
      break;
  }
?>

This patch changes case 1 to the following

<?php
      $footer = variable_get('site_footer', FALSE);
      if (module_exists('block')) {
        $footer_blocks = block_get_blocks_by_region('footer');
        $footer .= "\n" . drupal_render($footer_blocks);
      }

?>