[Form] Fix the default validator

src/Symfony/Component/Form/Extension/Core/Validator/DefaultValidator.php

@@ -31,18 +31,20 @@ class DefaultValidator implements FormValidatorInterface
             $length = (int) $_SERVER['CONTENT_LENGTH'];
             $max = trim(ini_get('post_max_size'));
 
-            switch (strtolower(substr($max, -1))) {
-                // The 'G' modifier is available since PHP 5.1.0
-                case 'g':
-                    $max *= 1024;
-                case 'm':
-                    $max *= 1024;
-                case 'k':
-                    $max *= 1024;
-            }
-
-            if ($length > $max) {
-                $form->addError(new FormError('The uploaded file was too large. Please try to upload a smaller file'));
+            if ('' !== $max) {
+                switch (strtolower(substr($max, -1))) {
+                    // The 'G' modifier is available since PHP 5.1.0
+                    case 'g':
+                        $max *= 1024;
+                    case 'm':
+                        $max *= 1024;
+                    case 'k':
+                        $max *= 1024;
+                }
+
+                if ($length > $max) {
+                    $form->addError(new FormError('The uploaded file was too large. Please try to upload a smaller file'));
+                }
             }
         }
     }