bug #34041 [HttpKernel] fix wrong removal of the just generated container dir (nicolas-grekas)

This PR was merged into the 3.4 branch.

Discussion
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[HttpKernel] fix wrong removal of the just generated container dir

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       | -
| License       | MIT
| Doc PR        | -

The patch applies to 3.4 but the fix really affects to 4.4 with the introduction of the new `.preload.php` file.

/cc @fabpot since you encountered this error quite often recently during `composer up/req` :)

Commits
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4ad09ebafb [HttpKernel] fix wrong removal of the just generated container dir

src/Symfony/Component/HttpKernel/Kernel.php

@@ -868,7 +868,7 @@ abstract class Kernel implements KernelInterface, RebootableInterface, Terminabl
             $fs->dumpFile($dir.$file, $code);
             @chmod($dir.$file, 0666 & ~umask());
         }
-        $legacyFile = \dirname($dir.$file).'.legacy';
+        $legacyFile = \dirname($dir.key($content)).'.legacy';
         if (file_exists($legacyFile)) {
             @unlink($legacyFile);
         }