[BUGFIX] Avoid accessing null-row

With `fallbackType` set to strict, only translated content is rendered.

In AbstractMenuContentObject->sectionIndex content is fetched and
overlayed. Once there is an element untranslated, the record overlay
will return a $row = `null`.

To mitigate, move all left over access to $row inside
the guarded if-block.

Resolves: #98043
Releases: main, 11.5
Change-Id: If4baf0fb88292cb8c6814539cf7efa610ae850f3
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/76673


Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>