[BUGFIX] Issue #3566: Check rootline for feGroups from page with extendToSubpages set

[timhorstmann]

What this pr does

When fetching usergroups to build a TSFE, the fe_groups field from current page could be empty. But there might be a page in the rootline with feGroups and extendToSubpages set.

This PR collects the feGroups from the rootline in this case.
The code is inspired from TYPO3\CMS\Backend\Utility\BackendUtility::ADMCMD_previewCmds

How to test

See #3566

Fixes: #3566

[dkd-kaehm]

@timhorstmann
Please check the implementation.
There is trouble with $pageInfo variable which is not defined.

[timhorstmann]

@dkd-kaehm Yes. Thank you for noticing. I updated the PR.

[timhorstmann]

This does not work as aspected.
$pageRecord['uid'] is not present. If i fix this, the page is not removed from the index queue, but still can't be found. I will update the PR.

[timhorstmann]

@dkd-kaehm We had a sideeffect with another issue with our customer. Took me a while to sort things out and have this tested from our test-team. I am confident that my PR is fine now.

I'm a little confused by the last comment. Is there another TODO for me?

[dkd-kaehm]

I'm a little confused by the last comment. Is there another TODO for me?

You mean following?:

Please check the implementation.
There is trouble with $pageInfo variable which is not defined.

If so, you answered and fixed it already.