Don't print "title" headline if no title is set in _wp_die_handler_exit() / _wp_die_handler_txt()

[ocean90]

$title is an optional argument for wp_die() and may therefore not be set. In such cases the title headline shouldn't be printed.

Example:

❯ composer run test
> @php ./vendor/phpunit/phpunit/phpunit
PHP Warning:  mysqli_real_connect(): (HY000/2002): Connection refused in src/wp-includes/wp-db.php on line 1633

wp_die called
Message: <p><code>Connection refused</code></p>
<h1>Error establishing a database connection</h1>
<p>This either means that the username and password information in your <code>wp-config.php</code> file is incorrect or we can&#8217;t contact the database server at <code>127.0.0.1</code>. This could mean your host&#8217;s database server is down.</p>
<ul>
<li>Are you sure you have the correct username and password?</li>
<li>Are you sure you have typed the correct hostname?</li>
<li>Are you sure the database server is running?</li>
</ul>
<p>If you&#8217;re unsure what these terms mean you should probably contact your host. If you still need help you can always visit the <a href="https://wordpress.org/support/forums/">WordPress Support Forums</a>.</p>

Title:

[ocean90]

In 47882:

Build/Test Tools: Avoid an empty "title" heading if no title is set in _wp_die_handler_exit() and _wp_die_handler_txt().

Fixes #50297.