[BUGFIX] Root node in folder tree in ElementBrowser works again

[BUGFIX] Root node in folder tree in ElementBrowser works again

The root node can be collapsed again without reloading the whole
ElementBrowser and killing its functionality.

Expanding the node works now too.

Releases: master
Resolves: #68486
Change-Id: I67e19c82302bb4df85153862ce07d2507d15865e
Reviewed-on: http://review.typo3.org/41989
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>