[BUGFIX] Fix faulty negation in FileInfo implementation

A faulty negation in the FileInfo class could end in a fatal
error if `finfo` is not supported by the php version and ends up
in not using `finfo` but `mime_content_type` if `finfo` is
supported.

Resolves: #65329
Releases: master
Change-Id: I768d70501ee4a8f03317563cef2d95e59e791e7d
Reviewed-on: http://review.typo3.org/37205


Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>