If there are no AMP-enabled taxonomies, don't count them.
If there are no AMP-enabled taxonomies, don't count them.

Before, there was an issue when
$amp_enabled_taxonomies was an empty array().
Then, the WP_Term_Query() returned terms
from all taxonomies.
So simply don't run the query if there
are no AMP-enabled taxonomies.

ampproject/amp-toolbox-php,ampproject/amp-toolbox-php