[BUGFIX] Remove empty values from intExplode in TreeController

intExplode missed an additional parameter which prevents the method 
from returning array with empty element.

Now when doktypesToShowInNewPageDragArea is empty, 
PageTree API will return empty array.

Resolves: #83542
Releases: master
Change-Id: I0ebfaef8e1ea782580e0feda59958bb39b0ca483
Reviewed-on: https://review.typo3.org/55335


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>