[5.6] Render the right view when using Mailables for sending mails ju…

…st in plain text format (#23981)

* Render the right view when sending mails just in plain text format (#23822)

* formatting

* Fixed code duplication

src/Illuminate/Mail/Mailer.php

@@ -201,7 +201,7 @@ public function render($view, array $data = [])
 
         $data['message'] = $this->createMessage();
 
-        return $this->renderView($view, $data);
+        return $this->renderView($view ?: $plain, $data);
     }
 
     /**