[BUGFIX] Page Tree not always updated after workspace actions

After some workspace actions being performed in the workspaces
module in the TYPO3 Backend, the page tree does not get updated:
* discarding a single workspace version
* performing mass actions which output warnings

Resolves: #59828
Releases: 6.2, master
Change-Id: Ic9fb6613e8647ed351246ea18fcb3696e60ef7b2
Reviewed-on: http://review.typo3.org/31091
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Oliver Hader <oliver.hader@typo3.org>