Error is like:
```
(SWT:339274): Gtk-CRITICAL **: 17:08:42.533: gtk_widget_compute_point:
assertion 'GTK_IS_WIDGET (widget)' failed
```

The problem comes from Control.getSurfaceOrigin method relying on
fixedHandle (even when there is not one) use
eventHandle() in this case.

Tested with Snippet165.