Multiple Screenshares: When exiting "maximise mode", the shown screenshare switches back to the first one

### Steps to reproduce

1. Have an ongoing call with multiple screenshares
2. Switch to the second screenshare
3. Maximize the screenshare
4. Exit maximize mode

### Outcome

#### What did you expect?
The selected screenshare should be minimized

#### What happened instead?
The shown screenshare switched back to the first screenshare.

Happens on 0.15.0 and previous versions.