[gnote] Make ignote() const

[Aurimas Černius <aurimasc src gnome org>]

commit 7b09e5ef0c5146c98fc8c529e3b49bd723cba635
Author: Aurimas Černius <aurisc4 gmail com>
Date:   Sun Dec 15 13:59:49 2019 +0200

    Make ignote() const

 src/abstractaddin.hpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/src/abstractaddin.hpp b/src/abstractaddin.hpp
index 7616431f..60094acc 100644
--- a/src/abstractaddin.hpp
+++ b/src/abstractaddin.hpp
@@ -49,9 +49,9 @@ public:
   bool is_disposing() const
     { return m_disposing; }
 
-  IGnote & ignote()
+  IGnote & ignote() const
     {
-      return *m_gnote;
+      return const_cast<IGnote&>(*m_gnote);
     }
 protected:
   virtual void dispose(bool disposing);