Don't only use ch != 0 to check if a character is a control char.

https://bugzilla.gnome.org/show_bug.cgi?id=644976

gtk/gtkimmulticontext.c

@@ -355,7 +355,7 @@ gtk_im_multicontext_filter_keypress (GtkIMContext *context,
       gunichar ch;
 
       ch = gdk_keyval_to_unicode (event->keyval);
-      if (ch != 0)
+      if (ch != 0 && !g_unichar_iscntrl (ch))
         {
           gint len;
           gchar buf[10];