[BUGFIX] Avoid undefined array key for bodyTagCObject

Fix warning if bodyTagCObject is referenced in TypoScript template.
Set as empty array.

Resolves: #98611
Releases: main, 11.5
Change-Id: Iaf0f3c1ae78386b2e6d5290251246740ee3d7d13
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/76065


Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>