[gnome-builder] ide-tree-builder: fix incomplete g_return

[Sébastien Lafargue <slafargue src gnome org>]

commit 936efd085c7d57f1fde514f919d06b9615487298
Author: Sebastien Lafargue <slafargue gnome org>
Date:   Tue Jan 19 19:14:40 2016 +0100

    ide-tree-builder: fix incomplete g_return

 libide/ide-tree-builder.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/libide/ide-tree-builder.c b/libide/ide-tree-builder.c
index af8176e..f7b2122 100644
--- a/libide/ide-tree-builder.c
+++ b/libide/ide-tree-builder.c
@@ -133,7 +133,7 @@ _ide_tree_builder_set_tree (IdeTreeBuilder *builder,
        IdeTreeBuilderPrivate *priv = ide_tree_builder_get_instance_private (builder);
 
        g_return_if_fail (IDE_IS_TREE_BUILDER (builder));
-       g_return_if_fail (priv->tree == NULL);
+       g_return_if_fail (priv->tree == NULL || IDE_IS_TREE (priv->tree));
        g_return_if_fail (IDE_IS_TREE (tree));
 
   if (priv->tree != tree)