[mutter] backends/native: Protect against NULL pointer constraints

[Marge Bot <marge-bot src gnome org>]

commit 904d7fa79899066865c6c9bf1a73762b6158ada8
Author: Olivier Fourdan <ofourdan redhat com>
Date:   Mon Dec 21 13:25:28 2020 +0100

    backends/native: Protect against NULL pointer constraints
    
    To clear a pointer constraint, the Wayland backend passes a NULL
    constraint to the native input backend.
    
    The new async API however tries to reference/un-reference the given
    object to use it while running in a separate task, which leads to a
    warning from GLib trying to g_object_ref()/g_object_unref() a non
    GObject pointer.
    
    To avoid that issue, simply set the data only if the given constraints
    pointer is not NULL.
    
    Suggested-by: Carlos Garnacho <carlosg gnome org>
    Closes: https://gitlab.gnome.org/GNOME/mutter/-/issues/1587
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1652>

 src/backends/native/meta-seat-impl.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/src/backends/native/meta-seat-impl.c b/src/backends/native/meta-seat-impl.c
index 904a9079f6..a9c0053b84 100644
--- a/src/backends/native/meta-seat-impl.c
+++ b/src/backends/native/meta-seat-impl.c
@@ -3333,7 +3333,8 @@ meta_seat_impl_set_pointer_constraint (MetaSeatImpl              *seat,
   g_return_if_fail (META_IS_SEAT_IMPL (seat));
 
   task = g_task_new (seat, NULL, NULL, NULL);
-  g_task_set_task_data (task, g_object_ref (constraint_impl), g_object_unref);
+  if (constraint_impl)
+    g_task_set_task_data (task, g_object_ref (constraint_impl), g_object_unref);
   meta_seat_impl_run_input_task (seat, task,
                                  (GSourceFunc) set_pointer_constraint);
   g_object_unref (task);