[BUGFIX] Add variable declaration in TsConfigParser

In backend/Classes/Configuratio/TsConfigParser.php $this->id is used,
but there was no variable declaration.

Resolves: #65443
Releases: master
Change-Id: I9bf72ab953f0fcd266c37867ba472fbdaff35077
Reviewed-on: http://review.typo3.org/37442


Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>