Prevent serving 500 error template when WordPress is serving response via wp_die()

[westonruter]

When wp_die() is called by default it sends a 500 status. This is done (probably incorrectly, as 400 is more appropriate) when trying to re-trash an already-trashed post. Clearly this is not the right use of the 500.php template:

We need to skip serving the 500.php template in this case.