actionmuxer: Add a precondition

This helps with debugging the inspectors action
handling.

diff --git a/gtk/gtkactionmuxer.c b/gtk/gtkactionmuxer.c
index 5fe2916dfdc6d9a989c4b56ffd783a71f3c82406..33e8c0542dffbe4d4f9ca6ac5422a58bb9a99c20 100644 (file)
--- a/gtk/gtkactionmuxer.c
+++ b/gtk/gtkactionmuxer.c
@@ -232,6 +232,8 @@ gtk_action_muxer_list_actions (GtkActionMuxer *muxer,
   GHashTable *actions;
   char **keys;
 
+  g_return_val_if_fail (GTK_IS_ACTION_MUXER (muxer), NULL);
+
   actions = g_hash_table_new_full (g_str_hash, g_str_equal, g_free, NULL);
 
   for ( ; muxer != NULL; muxer = muxer->parent)