bug #33568 [Validator] don't change state in case of exception (xabbuh)

This PR was merged into the 4.4 branch.

Discussion
----------

[Validator] don't change state in case of exception

| Q             | A
| ------------- | ---
| Branch?       | 4.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       |
| License       | MIT
| Doc PR        |

Commits
-------

dcd4733 don't change state in case of exception

Author: fabpot

src/Symfony/Component/Validator/ValidatorBuilder.php

@@ -255,12 +255,12 @@ public function setMetadataCache(CacheInterface $cache)
      */
     public function setMappingCache(CacheItemPoolInterface $cache)
     {
-        $this->mappingCache = $cache;
-
         if (null !== $this->metadataFactory) {
             throw new ValidatorException('You cannot set a custom mapping cache after setting a custom metadata factory. Configure your metadata factory instead.');
         }
 
+        $this->mappingCache = $cache;
+
         return $this;
     }