data-device: fix crash when a client dies during a drag with an icon
data-device: fix crash when a client dies during a drag with an icon

The commit that split wl_input_device into wl_seat and friends changed
erroneously the drag icon destroy listener, causing it to operate into
an invalid pointer to a wl_seat.

tulcod/wayland,eyolfson/wayland,tulcod/wayland,abooij/wayland,bitfactor/wayland,mchalupa/wayland,abooij/wayland,sir-murray/wayland,bitfactor/wayland,abooij/wayland,mchalupa/wayland,eyolfson/wayland,sir-murray/wayland,mchalupa/wayland,eyolfson/wayland,bitfactor/wayland,sir-murray/wayland,tulcod/wayland