XML Sitemap Custom allows duplicate entries

I have the same problems with 7.x-2.0.
Please fix it because is very huge for google!

This problem is not restricted to XML sitemap custom - XML sitemap node and XML sitemap menu are quite capable of duplicating each other's links as well!

Maybe this patch could be adapted to prevent duplicate links from being added to the index no matter which submodule is adding them? It's not much use just having XML sitemap custom checking if a link is a duplicate before adding it, if the menu and node submodules are still duplicating each other's entries! And if it can be, then this support issue could be merged with #2257191: Remove duplicate links when using both menu and node sitemap, which is about duplicates caused by those two.

The 6 year old patch in #9 to xmlsitemap_custom.admin.inc and xmlsitemap_custom.test does not apply to the latest xmlsitemap 7.x-2.x-dev and if still applicable needs a reroll.

Checking patch xmlsitemap_custom/xmlsitemap_custom.admin.inc...
error: while searching for:
    $menu_item['access'] = FALSE;
  }

  if (db_query_range("SELECT 1 FROM {xmlsitemap} WHERE type <> 'custom' AND loc = :loc AND status = 1 AND access = 1 AND language IN (:languages)", 0, 1, array(':loc' => $link['loc'], ':languages' => array(LANGUAGE_NONE, $link['language'])))->fetchField()) {
    form_set_error('loc', t('There is already an existing link in the sitemap with the path %link.', array('%link' => $link['loc'])));
  }
  elseif (empty($menu_item['access']) && !is_readable('./' . $link['loc'])) {

error: patch failed: xmlsitemap_custom/xmlsitemap_custom.admin.inc:146
error: xmlsitemap_custom/xmlsitemap_custom.admin.inc: patch does not apply

Checking patch xmlsitemap_custom/xmlsitemap_custom.test...
error: while searching for:
    $this->assertText('The custom link for system/files was saved');
    $this->assertSitemapLinkValues('custom', $link['id'], array('priority' => 0.1, 'changefreq' => XMLSITEMAP_FREQUENCY_ALWAYS, 'access' => 1, 'status' => 1));

    $this->clickLink('Delete');
    $this->drupalPost(NULL, array(), t('Delete'));
    $this->assertText('The custom link for system/files has been deleted.');
    $this->assertNoSitemapLink(array('type' => 'custom', 'loc' => 'system/files'));
  }

  /**

error: patch failed: xmlsitemap_custom/xmlsitemap_custom.test:68
error: xmlsitemap_custom/xmlsitemap_custom.test: patch does not apply