Fix for issue #10399

This fixes an issue in Symfony\Component\Config\Loader\FileLoader

| Q             | A
| ------------- | ---
| Bug fix?      |  yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |  #10339
| License       | MIT
| Doc PR        |  none