Add DICOM SEG workaround as specified in T29431

Summary:
Allows the repeated loading and saving of DICOM SEG files in
segmantation task lists.

Fixes T29431

Test Plan: Manual. Loaded both non-DICOM data and DICOM data provided by Hanno. Can confirm that the workaround allows repeated saving of DICOM SEGs whereas it does not work without the workaround.

Reviewers: floca, O3 MITK Reviewer Group II

Reviewed By: floca, O3 MITK Reviewer Group II

Subscribers: gaoh

Maniphest Tasks: T29431

Differential Revision: https://phabricator.mitk.org/D770