Updated Simple Sitemap logic to avoid errors.

[kepol]

See details in Drupal.org issue:

https://www.drupal.org/project/quantcdn/issues/3388797
https://www.drupal.org/project/quantcdn/issues/3418240

Added another sitemap with the default xsl generator and it looks like this:

kristens-mbp:quantcdn kristenpol$ qrunq
Forking seed worker.
Using drush binary at /var/www/html/vendor/bin/drush. Override with $DRUSH_PATH if required.
 [notice] [route_item] /node/1
 [notice] [route_item] /node/3
 [notice] [route_item] /node/2
 [notice] [route_item] /
 [notice] [route_item] /sitemaps/whatever/sitemap.xml
 [notice] [route_item] /sitemap_generator/default/sitemap.xsl
 [notice] [route_item] /sitemap.xml
 [success] Processed 1 items from the quant_seed_worker queue in 2.42 sec.
 [success] Processed 1 items from the quant_seed_worker queue in 2.73 sec.
 [success] Processed 2 items from the quant_seed_worker queue in 2.85 sec.
 [success] Processed 1 items from the quant_seed_worker queue in 3.2 sec.
 [success] Processed 2 items from the quant_seed_worker queue in 3.67 sec.
Seeding complete.