bug symfony#23231 Improved the exception page when there is no message (javiereguiluz)

This PR was merged into the 3.3 branch.

Discussion
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Improved the exception page when there is no message

| Q             | A
| ------------- | ---
| Branch?       | 3.3
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | symfony#23135
| License       | MIT
| Doc PR        | -

Commits
-------

5a18553 Improved the exception page when there is no message

Author: fabpot

src/Symfony/Bundle/TwigBundle/Resources/views/Exception/exception.html.twig

@@ -13,6 +13,7 @@
             </h2>
         </div>
     </div>
+    {% if exception.message is not empty %}
     <div class="container">
         <div class="exception-message-wrapper">
             <h1 class="break-long-words exception-message {{ exception.message|length > 180 ? 'long' }}">
@@ -24,6 +25,7 @@
             </div>
         </div>
     </div>
+    {% endif %}
 </div>
 
 <div class="container">