Include safe guards in services for cases where no reader was found; Removed exception in QmitkIOUtil. Message box is enough. Otherwise workbench would chrash with uncached exception.

Summary: Signed-off-by: Ralf Floca <r.floca@dkfz-heidelberg.de>

Test Plan: Checklists and try to load dicom files with trailing '.' on linux.

Reviewers: goch, kislinsk

Reviewed By: kislinsk

Maniphest Tasks: T20203

Differential Revision: https://phabricator.mitk.org/D16