Two local-test variants for mutter!5375: the NULL-check fix with
g_message traces, and Jonas Ådahl's proposal to forget a cancelled
touch sequence. They log which path cancelled the touch, to answer
how a resize reaches touch_can_grab_surface() with no focus surface.
Not applied yet; desktop.nix still uses mutter-touch-cancelled-grab.
Assisted-by: Claude:opus-5-5
