Mastodon may freeze with overlay visibility track of focused vertex

[stefanhahmann]

Steps to reproduce

1. Create a new Mastodon project using https://github.com/mastodon-sc/mastodon-example-data/blob/master/tgmm-mini/datasethdf5.xml and https://github.com/mastodon-sc/mastodon-example-data/blob/master/tgmm-mini/datasethdf5.h5
2. Open BDV
3. Track a few spots using a button in the BDV
4. Ensure that last tracked spot is focused and highlighted (i.e. pink + solid line, cf. video below) and the mouse pointer is inside this spot.
5. Stop moving the mouse
6. Use button v to set Overlay visibility to Track of focused vertex
7. Press button a
8. Mastodon is now "Frozen", i.e. Menus cannot be accessed anymore. Even Fiji cannot be closed properly.