[libadwaita] status-page: Add a missing check

[Alexander Mikhaylenko <alexm src gnome org>]

commit b00537e41fc43cd77fc3b037f4738601933b6452
Author: Adrien Plazas <kekun plazas laposte net>
Date:   Fri Oct 8 09:54:26 2021 +0200

    status-page: Add a missing check

 src/adw-status-page.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/src/adw-status-page.c b/src/adw-status-page.c
index 53053efd..d76455ae 100644
--- a/src/adw-status-page.c
+++ b/src/adw-status-page.c
@@ -294,6 +294,8 @@ adw_status_page_new (void)
 const char *
 adw_status_page_get_icon_name (AdwStatusPage *self)
 {
+  g_return_val_if_fail (ADW_IS_STATUS_PAGE (self), NULL);
+
   return self->icon_name;
 }