[gtk] listbox: Fix compiler warning

[Timm Bäder <baedert src gnome org>]

commit f9a589c7fd0e9b38f6e5cb2447159dea574b284d
Author: Timm Bäder <mail baedert org>
Date:   Sat Apr 13 06:26:17 2019 +0200

    listbox: Fix compiler warning

 gtk/gtklistbox.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gtk/gtklistbox.c b/gtk/gtklistbox.c
index bde8540dc7..5ad3d5950f 100644
--- a/gtk/gtklistbox.c
+++ b/gtk/gtklistbox.c
@@ -3659,7 +3659,7 @@ gtk_list_box_get_show_separators (GtkListBox *box)
 {
   GtkListBoxPrivate *priv = BOX_PRIV (box);
 
-  g_return_if_fail (GTK_IS_LIST_BOX (box));
+  g_return_val_if_fail (GTK_IS_LIST_BOX (box), FALSE);
 
   return priv->show_separators;
 }