[gtk+] gtksettings: Add a debug message if there is no default GtkSettings

[Philip Withnall <pwithnall src gnome org>]

commit 80b10aa1bd8b49a24940088f1949abbd213196d4
Author: Philip Withnall <withnall endlessm com>
Date:   Thu Feb 9 17:17:05 2017 +0000

    gtksettings: Add a debug message if there is no default GtkSettings
    
    Make it slightly more obvious when things are about to slide sideways
    because a NULL GtkSettings has been returned to a caller. This is a
    valid return value, but is rarely handled correctly.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=778382

 gtk/gtksettings.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/gtk/gtksettings.c b/gtk/gtksettings.c
index ee0a081..3bdb863 100644
--- a/gtk/gtksettings.c
+++ b/gtk/gtksettings.c
@@ -1281,8 +1281,10 @@ gtk_settings_get_default (void)
 
   if (display)
     return gtk_settings_get_for_display (display);
-  else
-    return NULL;
+
+  g_debug ("%s() returning NULL GtkSettings object. Is a display available?",
+           G_STRFUNC);
+  return NULL;
 }
 
 static void