GUI: clear stack widget in Data view in no data is selected

1. Go to Data view, add data.
2. Unselect data by clicking on the canvas.
3. Delete data by button
4. Try to interact (e.g. zoom) with remaining plot --> CRASH

changed milestone to %21 GUI fixes

added GUI crash labels

assigned to @m.svechnikov

mentioned in merge request !1297 (merged)

closed with merge request !1297 (merged)