[Form] [Validator] Fixed post_max_size = 0 bug (Issue symfony#8065)

Author: Stefan Oderbolz

src/Symfony/Component/Form/Extension/Validator/Constraints/FormValidator.php

@@ -126,7 +126,7 @@ public function validate($form, Constraint $constraint)
  if ($form->isRoot() && null !== $length) {
  $max = $this->serverParams->getPostMaxSize();
 
- if (null !== $max && $length > $max) {
+ if (!empty($max) && $length > $max) {
  $this->context->addViolation(
  $config->getOption('post_max_size_message'),
  array('{{ max }}' => $this->serverParams->getNormalizedIniPostMaxSize()),

src/Symfony/Component/Form/Tests/Extension/Validator/Constraints/FormValidatorTest.php

@@ -520,6 +520,7 @@ public function getPostMaxSizeFixtures()
  array(1024, '1K', 0, null),
  array(null, '1K', 0, null),
  array(1024, '', 0, null),
+ array(1024, 0, 0, null),
  );
  }