fixes usage of mb_*

src/Symfony/Component/Console/Application.php

@@ -720,7 +720,11 @@ class Application
     {
         $strlen = function ($string)
         {
-            return function_exists('mb_strlen') ? mb_strlen($string, mb_detect_encoding($string)) : strlen($string);
+            if (false === $encoding = mb_detect_encoding($string)) {
+                return strlen($string);
+            }
+
+            return function_exists('mb_strlen') ? mb_strlen($string, $encoding) : strlen($string);
         };
 
         do {