Correctly show preview nodes
Summary: Set the label of the preview node to visible
Test Plan:
manual UI testing
- open MITK, open the Segmentation plugin view
- load an image, create a segmentation node
- create a label and hide it
- open e.g. the Threshold-tool to create a preview
-> see how the preview can be seen (outline)
Reviewers: kislinsk, s434n, O1 MITK Reviewer Group I, floca
Reviewed By: s434n, O1 MITK Reviewer Group I, floca
Subscribers: floca, kalali, s434n, kislinsk
Maniphest Tasks: T29142
Differential Revision: https://phabricator.mitk.org/D651