[BUGFIX] Do not render <li> in section menu when CE has no header

Section menu is now not rendering empty <li> when CE has no header.

Resolves: #82099
Releases: master, 8.7
Change-Id: I095be0050ac9fa6c4a70ea4d4c942c01def0432f
Reviewed-on: https://review.typo3.org/53694


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>