[BUGFIX] Render empty icon instead of invalid identifier

This additionally resolves a display bug, since the
elements without an icon were moving to the left
and are now properly in line with the elements,
having an icon.

Resolves: #104558
Related: #103663
Releases: main
Change-Id: I0dc0c0affc1c206a3fa83981804cf818ea51fed3
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/85535


Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>