
When a drag was performed but did not finish successfully, e.g. because no mimetype was accepted, we need to send the source cancel event so clients know they can destroy the drag source (since version 3). Fixes https://gitlab.gnome.org/GNOME/mutter/issues/740 https://gitlab.gnome.org/GNOME/mutter/merge_requests/1031 (cherry picked from commit 6cc748cce9bb7cb47a4098cdc251c554d9f99b6b)