Update file SMTPMailSystem.php

Added code suggested by chrbak

Closes #3194372

src/Plugin/Mail/SMTPMailSystem.php

@@ -435,9 +435,9 @@ class SMTPMailSystem implements MailInterface, ContainerFactoryPluginInterface {
           // Only add a "reply-to" if it's not the same as "from".
           $reply_to_comp = $this->getComponents($value);
           $reply_to_email = $reply_to_comp['email'];
-          if ($reply_to_email !== $from) {
+          if ($reply_to_email && $reply_to_email !== $from) {
             $mailer->AddReplyTo($reply_to_email, $reply_to_comp['name']);
-          }
+          }          
           break;
 
         case 'sender':