Found posts not filled correctly

[Rahe]

Hi,

When i perform a custom WP_Query with the query 'fields'=>'ids' the found_posts is always 0 even if i have multiple pages of content like :

$q = new WP_Query( 
  array( 
   'posts_per_page' => 1,
   'fields' => 'ids'
  ) 
); 

var_dump( $q->found_posts );

If i just remove the fields index, the found_posts is correct.

Related: #14426, #17066

closed #21733 as a dupe. Patch handles all cases anyways. Attached.

Sergey's patch on #14426 does the same thing