[TASK] Improve comments and readability in PageArgumentValidator

Make clear that the early-bail out for empty pageArguments is
done to prevent setting `disableCaches` to `true`.

Also makes that that the $pageNotFoundOnCacheHashError
condition is really tied to pageArguments being non-empty.
Prevents us from refactoring that code and missing this bit.

Resolves: #99860
Related: #99859
Releases: main, 11.5, 10.4
Change-Id: I98ffa3dffe76a37970784979a2c4f2a9a64aa5bf
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77752


Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Benjamin Franzke <bfr@qbus.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: Benjamin Franzke <bfr@qbus.de>