SettingsSidePanel: implement deselect function

Gitlab: #1130

Change-Id: I166d41f495278a8d8a7c918e1d6d818108acae4e

src/app/settingsview/SettingsSidePanel.qml

@@ -143,11 +143,15 @@ SidePanelBase {
     }
 
     function open(index) {
-        indexSelected(-1)
         indexSelected(index)
         root.currentIndex = index
     }
 
+    function deselect() {
+        indexSelected(-1);
+        root.currentIndex = -1;
+    }
+
     function select(index) {
         if (!root.isSinglePane)
             indexSelected(index)