After importing a previous config from a snapshot, the snapshots list is populated with duplicates

[emtiu]

When testing for #1508, I noticed a bug in the current dev code that I had previously encountered in the wild.

After importing a previous config from a snapshot, the snapshots list is populated with duplicates. They disappear after the GUI has been restarted once.

Steps to reproduce:

1. Start the GUI with no configuration.
2. Choose "Yes" to restore a previous configuration.
3. Select a snapshot and click "Restore".
4. In the "Settings" dialog that opens now, click "OK" without making changes.
5. Observe how every snapshot is listed twice:

After quitting and restarting the GUI once, the snapshots are listed as expected, without duplicates:

I remember that this bug was quite a heart-stopper when I encountered it in the wild. I thought there was something wrong with the snapshots.

[buhtz]

I played around with debug code and inspect module. I followed some trails and ideas but I am still not sure. Qt's signal/slot mechanic seems to be involved somehow and the FillTimeLineThread class. But finally I don't get it.

Anyway, it is planned to refactor that code. So I am assuming the problem will be fade away somehow.