bug symfony#25753 [Console] Fix restoring exception handler (nicolas-grekas, fancyweb)

This PR was merged into the 3.4 branch.

Discussion
----------

[Console] Fix restoring exception handler

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | ,p
| Tests pass?   | yes
| Fixed tickets | symfony#25718
| License       | MIT
| Doc PR        | -

Commits
-------

0096449 [Console] Keep the modified exception handler
3fa1ad9 [Console] Fix restoring exception handler

Author: nicolas-grekas

src/Symfony/Component/Console/Application.php

@@ -163,10 +163,18 @@ public function run(InputInterface $input = null, OutputInterface $output = null
                 $exitCode = 1;
             }
         } finally {
+            // if the exception handler changed, keep it
+            // otherwise, unregister $renderException
             if (!$phpHandler) {
+                if (set_exception_handler($renderException) === $renderException) {
+                    restore_exception_handler();
+                }
                 restore_exception_handler();
             } elseif (!$debugHandler) {
-                $phpHandler[0]->setExceptionHandler(null);
+                $finalHandler = $phpHandler[0]->setExceptionHandler(null);
+                if ($finalHandler !== $renderException) {
+                    $phpHandler[0]->setExceptionHandler($finalHandler);
+                }
             }
         }