Ensure material is selected on first opening of material manager

resources/qml/Preferences/Materials/MaterialsPage.qml

@@ -53,7 +53,11 @@ Item
     }
 
     // When loaded, try to select the active material in the tree
-    Component.onCompleted: resetExpandedActiveMaterial()
+    Component.onCompleted:
+    {
+        resetExpandedActiveMaterial()
+        base.newRootMaterialIdToSwitchTo = active_root_material_id
+    }
 
     // Every time the selected item has changed, notify to the details panel
     onCurrentItemChanged: