Fixes two pie runtimes

Created by: 9600bauds

// NOTE FROM AMATEUR CODER WHO STRUGGLED WITH RUNTIMES // throw_impact is called multiple times when an item is thrown: see /atom/movable/proc/hit_check at atoms_movable.dm // Do NOT delete an item as part of it's throw_impact unless you've checked the hit_atom is a turf, as that's effectively the last time throw_impact is called in a single throw. // Otherwise, shit will runtime in the subsequent throw_impact calls.

Also, snacks/pie/empty had trash = null so shit would never delete itself.