Trackpanel accessibility: incorrect focus can be read

Problem: If the initial focus is a control in a toolbar, then after applying an effect such as amplify, then the focus is read as being a track, not the control in the toolbar. TrackPanelAx::SetFocus() can be called when the TrackPanel is not the focus, and send a focus event. Fix: In TrackPanelAx::SetFocus(), only send a focus event if the TrackPanel is the focus.