[BUGFIX] Prevent double assets folder

With the cleanup in https://review.typo3.org/46096/ double temp folders
were introduced for temporary image files. Now temporary files are
stored in typo3temp/assets/assets/images.

This patch resets the tempPath variable of the GraphicalFunctions class
to make sure only one assets folder is used.

Resolves: #75841
Releases: master
Change-Id: I968fab0175ba54037fa82d8721aca13f81d90c83
Reviewed-on: https://review.typo3.org/47834


Reviewed-by: Helmut Hummel <helmut.hummel@typo3.org>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Philipp Gampe <philipp.gampe@typo3.org>
Tested-by: Philipp Gampe <philipp.gampe@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>