Unable to filter term query args using `pre_get_terms` action

[jfarthing84]

Thus making the action practically useless. But fear not, there is a simple remedy. In fact, the same remedy is used in WP_Query::get_posts! Use a reference within WP_Term_Query::get_terms to access the query vars locally:

$args = &$this->query_vars;

[boonebgorges]

Good call. Thanks for the patch, @jfarthing84.

[boonebgorges]

In 39625:

Taxonomy: Ensure that mods to query vars in pre_term_query callbacks have an effect.

Previously, it was possible to modify the query_vars array, but
the changes would be ignored after pre_term_query had finished
running.

Props jfarthing84.
Fixes #39354.

[boonebgorges]

#39457 was marked as a duplicate.

[littler.chicken]

A note, changeset 39625 breaks code which works in 4.7 and earlier:

	$taxonomies = get_taxonomies();
	$args       = array( 'orderby' => 'count', 'order' => 'DESC' );
	$terms      = wp_get_object_terms( get_the_ID(), $taxonomies, $args );

It may be that this code is faulty and deserves to break (properly using get_object_taxonomies() works), but I thought I would mention it, in case I'm not the only one affected.

[boonebgorges]

#40551 was marked as a duplicate.