[gtk/gtk-3-24: 1/2] gkimmulticontext: Fix crash due to leaked signal handler

[Carlos Garnacho <carlosg src gnome org>]

commit 822705fe3e041f78ff411d58b34fc15689ecee0f
Author: Alexandr Miloslavskiy <alexandr miloslavskiy syntevo com>
Date:   Tue Dec 17 12:44:33 2019 +0100

    gkimmulticontext: Fix crash due to leaked signal handler
    
    The problem is caused by gtk_im_multicontext_set_slave(), which forgets
    to disconnect these signal handlers:
    * gtk_im_multicontext_retrieve_surrounding_cb
    * gtk_im_multicontext_delete_surrounding_cb
    
    If slave GtkImContext emits signal after GtkIMMulticontext context is
    destroyed, this leads to reading freed memory, sometimes causing a crash.
    
    Fixes: #2365

 gtk/gtkimmulticontext.c | 6 ++++++
 1 file changed, 6 insertions(+)
---
diff --git a/gtk/gtkimmulticontext.c b/gtk/gtkimmulticontext.c
index a8700a8c66..ec67254946 100644
--- a/gtk/gtkimmulticontext.c
+++ b/gtk/gtkimmulticontext.c
@@ -193,6 +193,12 @@ gtk_im_multicontext_set_slave (GtkIMMulticontext *multicontext,
       g_signal_handlers_disconnect_by_func (priv->slave,
                                            gtk_im_multicontext_commit_cb,
                                            multicontext);
+      g_signal_handlers_disconnect_by_func (priv->slave,
+                                           gtk_im_multicontext_retrieve_surrounding_cb,
+                                           multicontext);
+      g_signal_handlers_disconnect_by_func (priv->slave,
+                                           gtk_im_multicontext_delete_surrounding_cb,
+                                           multicontext);
 
       g_object_unref (priv->slave);
       priv->slave = NULL;