Code review comment for lp:~alan-griffiths/mir/drag-and-drop

18:37:58 11: [ RUN ] DragAndDrop.during_drag_when_user_moves_mouse_client_receives_handle
...
18:39:30 11: /<<BUILDDIR>>/mir-0.26.0+xenial4292bzr4108/tests/acceptance-tests/drag_and_drop.cpp:191: Failure
18:39:30 11: Value of: have_cookie.wait_for(receive_event_timeout)
18:39:30 11: Expected: is equal to true
18:39:30 11: Actual: false (of type bool)
18:39:30 11: ==27856== Invalid read of size 8

The memory errors and FD leaks that follow result from following the resulting nullptr.

~~~~

18:20:22 12: [ FAILED ] ClientLatency.dropping_latency_is_closer_to_zero_than_one
18:20:22 12: [ FAILED ] ClientLatency.async_swap_dropping_latency_is_closer_to_zero_than_one

lp:1640366