Coding Standards: Check for an empty mail server URL first in wp-mail.php.

This follows a common best practice of checking for an empty value before doing a specific comparison.

Follow-up to [39772].

Props dilipbheda, mukesh27.
Fixes #63219.

git-svn-id: https://develop.svn.wordpress.org/trunk@60122 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-mail.php

@@ -17,7 +17,7 @@
 
 $mailserver_url = get_option( 'mailserver_url' );
 
-if ( 'mail.example.com' === $mailserver_url || empty( $mailserver_url ) ) {
+if ( empty( $mailserver_url ) || 'mail.example.com' === $mailserver_url ) {
 	wp_die( __( 'This action has been disabled by the administrator.' ), 403 );
 }