Placing sound is played even when no slab is placed

[Mattatjahu]

I've noticed that when trying to place slabs somewhere they can't be placed (e.g. right inside the player's hitbox) the sound of placing a block is played. Although correctly no block is placed, both the animation (player's hand swinging) and the sound are triggered. It's just a minor inconvenience, but it can be irritating at times ^^ Besides that I've been enjoying this mod quite much!