[gtk+] Dialog: Clarify that response ID 0 is not reserved

[Daniel Boles <dboles src gnome org>]

commit 2cd65158a0253adf8bdca43588706889d0807969
Author: Daniel Boles <dboles src gnome org>
Date:   Sun Oct 8 22:19:13 2017 +0100

    Dialog: Clarify that response ID 0 is not reserved
    
    I only got so far in math, but it looks to me like zero isn’t positive.
    We don’t reserve it, so be clear about that.

 gtk/gtkdialog.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gtk/gtkdialog.h b/gtk/gtkdialog.h
index 505db6a..4786a49 100644
--- a/gtk/gtkdialog.h
+++ b/gtk/gtkdialog.h
@@ -67,7 +67,7 @@ typedef enum
  * @GTK_RESPONSE_HELP: Returned by Help buttons in GTK+ dialogs
  *
  * Predefined values for use as response ids in gtk_dialog_add_button().
- * All predefined values are negative, GTK+ leaves positive values for
+ * All predefined values are negative; GTK+ leaves values of 0 or greater for
  * application-defined response ids.
  */
 typedef enum