Cancels an ongoing drag operation on the source side.
If you want to be able to cancel a drag operation in this way, you need to keep a pointer to the drag context, either from an explicit call to drag_begin_with_coordinates, or by connecting to drag_begin.
If context does not refer to an ongoing drag operation, this function does nothing.
If a drag is cancelled in this way, the result argument of drag_failed
is set to GTK_DRAG_RESULT_ERROR.
| context |
a DragContext, as e.g. returned by drag_begin_with_coordinates |