minor #33016 [HttpKernel] Resilience against file_get_contents() race…

… conditions (derrabus)

This PR was merged into the 3.4 branch.

Discussion
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[HttpKernel] Resilience against file_get_contents() race conditions

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | N/A
| License       | MIT
| Doc PR        | N/A

This PR addresses #33007 (comment).

Commits
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5892837 Resilience against file_get_contents() race conditions.

src/Symfony/Component/HttpKernel/HttpCache/Store.php

@@ -356,7 +356,7 @@ private function load($key)
     {
         $path = $this->getPath($key);
 
-        return file_exists($path) ? file_get_contents($path) : null;
+        return file_exists($path) && false !== ($contents = file_get_contents($path)) ? $contents : null;
     }
 
     /**