[TASK] Fixed an exception that could occur when reading register.php files

Classes/Service/MailTemplateService.php

@@ -827,7 +827,7 @@ class MailTemplateService {
 			$extensionConfigDirectory = ExtensionManagementUtility::extPath($extension);
 			$extensionConfigDirectory .= self::CONFIG_PATH;
 
-			if (!\is_dir($extensionConfigDirectory)) {
+			if (!\is_file($extensionConfigDirectory . '/' . self::REGISTER_FILE)) {
 				continue;
 			}