[gimp] app: make an assertion more correct in GimpDrawableUndo

[Michael Natterer <mitch src gnome org>]

commit be66d1a2be7f3286fbf761afd6d5a7c4d78f53e8
Author: Michael Natterer <mitch gimp org>
Date:   Mon Nov 7 13:10:21 2016 +0100

    app: make an assertion more correct in GimpDrawableUndo

 app/core/gimpdrawableundo.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/app/core/gimpdrawableundo.c b/app/core/gimpdrawableundo.c
index 7c0f6f4..1af5aeb 100644
--- a/app/core/gimpdrawableundo.c
+++ b/app/core/gimpdrawableundo.c
@@ -112,7 +112,7 @@ gimp_drawable_undo_constructed (GObject *object)
   G_OBJECT_CLASS (parent_class)->constructed (object);
 
   g_assert (GIMP_IS_DRAWABLE (GIMP_ITEM_UNDO (object)->item));
-  g_assert (drawable_undo->buffer != NULL);
+  g_assert (GEGL_IS_BUFFER (drawable_undo->buffer));
 }
 
 static void