Filters changeset post data upon insert to ensure post_name is intact.

This is needed to prevent the post_name from being dropped when the post is
transitioned into pending status by a contributor.

function _wp_customize_changeset_filter_insert_post_data( $post_data, $supplied_post_data ) {
	if ( isset( $post_data['post_type'] ) && 'customize_changeset' === $post_data['post_type'] ) {

		// Prevent post_name from being dropped, such as when contributor saves a changeset post as pending.
		if ( empty( $post_data['post_name'] ) && ! empty( $supplied_post_data['post_name'] ) ) {
			$post_data['post_name'] = $supplied_post_data['post_name'];
		}
	}
	return $post_data;
}