Broken grilles will not spawn rods when hit

Eh, supposedly fixes https://github.com/tgstation/-tg-station/issues/4181, but now that I think about it, it says girders in the issue, not grilles, which might be a mistake or not. Either way, broken grilles don't spawn rods anymore when hit. healthcheck() was called every time in attackby(), now it will only spawn rod when grille is actually destroyed.

Diff looks weird, I added another check to prevent using glass on broken grille from creating a one-way window, because it's not immulsive, looks silly and you can do that anyway by standing on top of the tile.