When a variant of a variant is created, the varianfOf reference is badly set.

This issue can be reproduced in demoauthor running on Magnolia 6.1

To reproduce:

1. Go to https://demoauthor.magnolia-cms.com/.magnolia/admincentral#app:pages;/travel/about:edit
2. Choose a sub component of the column layout and create a component variant
3. Choose the surrounding column layout component and create a component variant
4. Choose a sub component of the parent variant and create a component variant 

In JCR browser the reference the mgnl:variationOf of the step 4 is wrong, it points to the original component ID.