[gimp] Use G_TYPE_CHECK_INSTANCE_TYPE() instead of GIMP_IS_ITEM()

[Michael Natterer <mitch src gnome org>]

commit 11ca58ccf24a132dd38d5070e9320c107275984c
Author: Michael Natterer <mitch gimp org>
Date:   Mon Feb 8 01:11:30 2010 +0100

    Use G_TYPE_CHECK_INSTANCE_TYPE() instead of GIMP_IS_ITEM()
    
    See below...

 app/core/gimpitemtree.c |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)
---
diff --git a/app/core/gimpitemtree.c b/app/core/gimpitemtree.c
index c581741..0020205 100644
--- a/app/core/gimpitemtree.c
+++ b/app/core/gimpitemtree.c
@@ -297,13 +297,14 @@ gimp_item_tree_set_active_item (GimpItemTree *tree,
   GimpItemTreePrivate *private;
 
   g_return_if_fail (GIMP_IS_ITEM_TREE (tree));
-  g_return_if_fail (item == NULL || GIMP_IS_ITEM (item));
 
   private = GIMP_ITEM_TREE_GET_PRIVATE (tree);
 
   g_return_if_fail (item == NULL ||
-                    (gimp_item_is_attached (item) &&
-                     gimp_item_get_image (item) == private->image));
+                    G_TYPE_CHECK_INSTANCE_TYPE (item, private->item_type));
+  g_return_if_fail (item == NULL || gimp_item_is_attached (item));
+  g_return_if_fail (item == NULL ||
+                    gimp_item_get_image (item) == private->image);
 
   if (item != private->active_item)
     {