[BUGFIX] Restore workspace filter in Belog module

The `workspacesExtensionLoaded` variable is
removed from the Template, since it is never set
and therefore always equals to FALSE.

The previous "is workspaces loaded" check is
now directly integrated in the already existing
`showWorkspaceSelector` check.

Resolves: #94017
Releases: master, 10.4
Change-Id: Ib63fa549028a875951b8940183b610f7943774f5
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/68910


Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benni Mack <benni@typo3.org>