Fix routes, README and some little changes in the controller

mails/themes/modern/README.md

@@ -1,6 +1,6 @@
 # Modern theme
 
-This theme was generated based on the MJML templates as they offer great responsiveness and guaranty that
+This theme was generated based on MJML templates as they offer great responsiveness and ensure that
 your templates will be readable in most mail viewers and mail web applications.
 
 The source MJML templates and the tool allowing to compile/convert them as twig templates can be found at:

src/PrestaShopBundle/Controller/Admin/Improve/International/MailLayoutController.php

@@ -43,7 +43,7 @@
  * This controller is used to preview mail templates from new theme. It uses the
  * same service used by the generator so it is a handy way to debug them.
  */
-class MailLayoutController extends FrameworkBundleAdminController
+final class MailLayoutController extends FrameworkBundleAdminController
 {
     /**
      * @param string $theme
@@ -93,19 +93,16 @@ private function renderLayout($themeName, $layoutName, $type, $locale = '', $mod
     {
         /** @var ThemeCatalogInterface $themeCatalog */
         $themeCatalog = $this->get(ThemeCatalogInterface::class);
-        try {
-            /** @var ThemeInterface $theme */
-            $theme = $themeCatalog->getByName($themeName);
-        } catch (InvalidArgumentException $e) {
-            throw new InvalidArgumentException($e->getMessage());
-        }
+        /** @var ThemeInterface $theme */
+        $theme = $themeCatalog->getByName($themeName);
 
         /** @var LayoutInterface $layout */
         $layout = null;
         /* @var LayoutInterface $layoutInterface */
         foreach ($theme->getLayouts() as $layoutInterface) {
-            if ($layoutInterface->getName() == $layoutName &&
-                (empty($module) || $layoutInterface->getModuleName() == $module)) {
+            if ($layoutInterface->getName() == $layoutName
+                && (empty($module) || $layoutInterface->getModuleName() == $module)
+            ) {
                 $layout = $layoutInterface;
                 break;
             }

src/PrestaShopBundle/Resources/config/routing/admin/improve/international/_international.yml

@@ -24,4 +24,4 @@ _tax:
 
 _mail_layout:
   resource: "mail_layout.yml"
-  prefix: /mail_layout/
+  prefix: /mail-layout/