bug #13403 [TwigBridge] exit when Twig environment is not set in the DebugCommand (xabbuh)

This PR was merged into the 2.7 branch.

Discussion
----------

[TwigBridge] exit when Twig environment is not set in the DebugCommand

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

The `DebugCommand` from the TwigBridge requires the `Twig_Environment`
to be set. Thus, if the `setTwigEnvironment()` were not called, the
command execution would have been aborted with a PHP error.

Commits
-------

1cfc1b7 exit when Twig environment is not set

src/Symfony/Bridge/Twig/Command/DebugCommand.php

@@ -83,6 +83,13 @@ EOF
     protected function execute(InputInterface $input, OutputInterface $output)
     {
         $twig = $this->getTwigEnvironment();
+
+        if (null === $twig) {
+            $output->writeln('<error>The Twig environment needs to be set.</error>');
+
+            return 1;
+        }
+
         $types = array('functions', 'filters', 'tests', 'globals');
 
         if ($input->getOption('format') === 'json') {