WORLDEDIT-3078 - Reported by sk89q

This causes operations to stop really early because many WE algorithms do it.

On previous versions of WE, the check ignored air. However, this also meant that //set 0 over a really large area of existing air would still block the game/server. Once we get proper multipass support though, this would become irrelevant.

Related to #825 most likely. Don't really know what the correct direction to take is, but right now it seems that the change limiter is too high up (prior to masking even!). We should probably take another pass at this when we move arranging off-thread.