[gtk+] Fix return value error in _gtk_window_get_popover_parent

[Ting-Wei Lan <lantw src gnome org>]

commit f85db624eb2bb0e6491ac7942433b65147a89696
Author: Ting-Wei Lan <lantw src gnome org>
Date:   Thu Jun 18 12:14:05 2015 +0800

    Fix return value error in _gtk_window_get_popover_parent

 gtk/gtkwindow.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/gtk/gtkwindow.c b/gtk/gtkwindow.c
index 555d9d7..fb8e0b0 100644
--- a/gtk/gtkwindow.c
+++ b/gtk/gtkwindow.c
@@ -11964,8 +11964,8 @@ _gtk_window_get_popover_parent (GtkWindow *window,
 {
   GtkWindowPopover *data;
 
-  g_return_if_fail (GTK_IS_WINDOW (window));
-  g_return_if_fail (GTK_IS_WIDGET (popover));
+  g_return_val_if_fail (GTK_IS_WINDOW (window), NULL);
+  g_return_val_if_fail (GTK_IS_WIDGET (popover), NULL);
 
   data = _gtk_window_has_popover (window, popover);