Bug 977056 - [Dialer] Visual discrepancies: Call ended view under conference call participants list

We should rather do something like:
```javascript
else if (this._wasUnmerged()) {
  if (!CallScreen.hasGroupDetailsDisplayed()) {
    // If the group details is not visible, move this call to the main screen
     CallScreen.insertCall(this.node);
  }
  this._leftGroup = false;
}
```