[BUGFIX] Enable icon for "Show Content From Page" for root page

When the root page is showing content from another page now the
correct "root" icon is displayed instead of the icon for normal
pages.

Resolves: #70617
Releases: master
Change-Id: I42d7aae521b40518d8087b004c44af02aeb9a177
Reviewed-on: https://review.typo3.org/44335


Reviewed-by: Benjamin Kott <info@bk2k.info>
Tested-by: Benjamin Kott <info@bk2k.info>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>