[BUGFIX] Initialize ExtendedFileUtility only if an actual upload happens

There is no need to initialize ExtendedFileUtility every request in
EXT:impexp. Check if an upload is actually performed.

Change-Id: I45ff2affd38cf00b3e182741749fb567f6853658
Resolves: #72692
Releases: master
Reviewed-on: https://review.typo3.org/45878


Reviewed-by: Susanne Moog <typo3@susannemoog.de>
Tested-by: Susanne Moog <typo3@susannemoog.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>