input-settings: Disconnect device signals on dispose

The input settings constructor installs callback functions on device
added/remove and tool-changed.

However, on dispose, those signals are not disconnected, meaning that on
teardown, once the devices get removed eventually, the callback will
still fire and call the callback with freed data, causing a crash.

Make sure we clear the signals on devices on dispose, to avoid the crash
on teardown.

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1438

src/backends/meta-input-settings.c

@@ -153,6 +153,8 @@ meta_input_settings_dispose (GObject *object)
   MetaInputSettings *settings = META_INPUT_SETTINGS (object);
   MetaInputSettingsPrivate *priv = meta_input_settings_get_instance_private (settings);
 
+  g_signal_handlers_disconnect_by_data (priv->seat, settings);
+
   g_clear_object (&priv->virtual_pad_keyboard);
 
   g_clear_object (&priv->mouse_settings);