[libgda] gda-tree: fix private implementation

[Daniel Espinosa Ortiz <despinosa src gnome org>]

commit 47fde3ea15164daf2723a4a6d0c9c95af12a075d
Author: Daniel Espinosa <esodan gmail com>
Date:   Sat Sep 8 19:33:29 2018 -0500

    gda-tree: fix private implementation

 libgda/gda-tree.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)
---
diff --git a/libgda/gda-tree.c b/libgda/gda-tree.c
index 6e3de28cc..35ac7be78 100644
--- a/libgda/gda-tree.c
+++ b/libgda/gda-tree.c
@@ -86,6 +86,8 @@ gda_tree_class_init (GdaTreeClass *klass)
 
        parent_class = g_type_class_peek_parent (klass);
 
+       g_type_class_add_private (object_class, sizeof (GdaTreePrivate));
+
        /* signals */
        /**
         * GdaTree::node-changed:
@@ -261,9 +263,6 @@ gda_tree_set_property (GObject *object,
                         G_GNUC_UNUSED const GValue *value,
                         GParamSpec *pspec)
 {
-       GdaTree *tree;
-
-       tree = GDA_TREE (object);
        switch (param_id) {
        default:
                G_OBJECT_WARN_INVALID_PROPERTY_ID (object, param_id, pspec);