bug symfony#29764 [HttpFoundation] Check file exists before unlink (adam-mospan)

This PR was submitted for the master branch but it was squashed and merged into the 3.4 branch instead (closes symfony#29764).

Discussion
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[HttpFoundation] Check file exists before unlink

Check file exists to prevent ErrorException

| Q             | A
| ------------- | ---
| Branch?       | 2.6 <!-- see below -->
| Bug fix?      | yes
| New feature?  | no <!-- don't forget to update src/**/CHANGELOG.md files -->
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no <!-- don't forget to update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | #...   <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | symfony/symfony-docs#... <!-- required for new features -->

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Commits
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1954187 [HttpFoundation] Check file exists before unlink

Author: nicolas-grekas

src/Symfony/Component/HttpFoundation/BinaryFileResponse.php

@@ -305,7 +305,7 @@ public function sendContent()
         fclose($out);
         fclose($file);
 
-        if ($this->deleteFileAfterSend) {
+        if ($this->deleteFileAfterSend && file_exists($this->file->getPathname())) {
             unlink($this->file->getPathname());
         }