Empty variation is created when saving changes in demo board game information

[bumbaaz]

It appears that an empty variation is created after saving changes in a demo board's game information.
The visualization also switches to this new variation and the old variation disappears from the branch visualizer.
After reloading the page the old variation reappears and the user can switch back to it and also remove the empty one... but even if no data is really lost during the bug, the user may end up thinking so.

Steps to reproduce the behavior:

1. Create a new demo board
2. Set up any position
3. From the right side menu go to 'game information', and press 'save'
4. Board gets empty

Thanks!

[anoek]

Related to #2821