meta_wayland_touch_cancel() clears focus_surface on active touches
but keeps their serials until the finger lifts. A client asking for
a move/resize grab with such a serial (anotherim-js's resize edges
by touch) makes touch_can_grab_surface() dereference NULL and takes
down gnome-shell (four crashes on 2026-10-13, same address).
Carry a one-line NULL check until nixpkgs' mutter has a fix; it is
not upstream as of mutter 50.2 / main.
Assisted-by: Claude:opus-5
Sergei Poljanski
1320decc26