If there are too many requests, file contents are no longer output because access is denied.

[Fraenkiman]

Reproducibility:
In a CLI test, I sent 33 requests.

The PHP log quickly filled up with information like this:
Note: file_get_contents(): Reading 8192 bytes failed with errno=13. Access denied in \flatpress-release-141-notturno\fp-includes\core\core.fileio.php on line 37.

[Fraenkiman]

Fixed with 0d4684e and 46736d1.