Duplicate landmark appears when deactivating transformed view

[mcfly3001]

A duplicate landmark is showing up when setting the first landmark (using Slicer 4.10.2). This behaviour though only shows up when the user unchecks the "Transformed" view before adding the first landmark.

So to reproduce, do the following:

1. Load two volumes
2. Select the Landmark Registration module
3. Set fixed and moving volume
4. Uncheck the "Transformed" checkbox in Display
5. Add a first landmark
6. Set the corresponding landmark
7. Try to move the first added landmark in the slice view --> A second landmark with same name shows up

It seems to be a minor bug as the registration anyways works as expected. The second landmark with same label though might confuse the user.

[lassoan]

@Sunderlandkyl please check this as well when you fix up Landmark Registration module for Slicer-4.11. Thank you!