[gtk/matthiasc/expression] expression: Don't rely on peeking

[Matthias Clasen <matthiasc src gnome org>]

commit 3dbed5e6081ec485c562c84a20e206a8c7170d6f
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu Nov 28 14:25:41 2019 -0500

    expression: Don't rely on peeking
    
    There is no guarantee that somebody else has refed
    the class yet, so do it here. This was causing test
    failures, when running single tests that happen to
    call this function early on.

 gtk/gtkexpression.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)
---
diff --git a/gtk/gtkexpression.c b/gtk/gtkexpression.c
index c80e6f60f1..a77d159097 100644
--- a/gtk/gtkexpression.c
+++ b/gtk/gtkexpression.c
@@ -552,11 +552,15 @@ gtk_property_expression_new (GType          this_type,
 
   if (g_type_is_a (this_type, G_TYPE_OBJECT))
     {
-      pspec = g_object_class_find_property (g_type_class_peek (this_type), property_name);
+      GObjectClass *class = g_type_class_ref (this_type);
+      pspec = g_object_class_find_property (class, property_name);
+      g_type_class_unref (class);
     }
   else if (g_type_is_a (this_type, G_TYPE_INTERFACE))
     {
-      pspec = g_object_interface_find_property (g_type_default_interface_peek (this_type), property_name);
+      GTypeInterface *iface = g_type_default_interface_ref (this_type);
+      pspec = g_object_interface_find_property (iface, property_name);
+      g_type_default_interface_unref (iface);
     }
   else
     {