[pygi] GTypeInterface cannot be unrefed

[Tomeu Vizoso <tomeuv src gnome org>]

commit aa0357e468eb91e0f3707346e9b32f312fbf51d3
Author: Tomeu Vizoso <tomeu sugarlabs org>
Date:   Thu Apr 29 13:06:15 2010 +0200

    GTypeInterface cannot be unrefed
    
    https://bugzilla.gnome.org/show_bug.cgi?id=617159

 gi/gimodule.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/gi/gimodule.c b/gi/gimodule.c
index 8650fb3..665c796 100644
--- a/gi/gimodule.c
+++ b/gi/gimodule.c
@@ -215,7 +215,9 @@ _wrap_pyg_hook_up_vfunc_implementation (PyObject *self, PyObject *args)
     }
 
     g_base_info_unref (struct_info);
-    g_type_class_unref (implementor_class);
+
+    if (!is_interface)
+        g_type_class_unref (implementor_class);
 
     Py_RETURN_NONE;
 }