[mutter] core: Fix memory selection source leak after clipboard owner disappears

[Carlos Garnacho <carlosg src gnome org>]

commit a031ac067e4b275d1de3ae7c018711be187fbb6b
Author: Sebastian Keller <skeller gnome org>
Date:   Fri Jun 5 19:18:43 2020 +0200

    core: Fix memory selection source leak after clipboard owner disappears
    
    When an app disappears after some data from it has been copied to the
    clipboard, the owner of the clipboard selection becomes a new memory
    selection source. The initial reference this new selection source is
    never unref'ed, which leads to this being leaked on the next clipboard
    selection owner change.
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1293

 src/core/meta-clipboard-manager.c | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/src/core/meta-clipboard-manager.c b/src/core/meta-clipboard-manager.c
index b85d87fd0d..69b00d85a8 100644
--- a/src/core/meta-clipboard-manager.c
+++ b/src/core/meta-clipboard-manager.c
@@ -152,6 +152,7 @@ owner_changed_cb (MetaSelection       *selection,
                                                     display->saved_clipboard);
       g_set_object (&display->selection_source, new_owner);
       meta_selection_set_owner (selection, selection_type, new_owner);
+      g_object_unref (new_owner);
     }
 }