issue re-occurrence

[MrGrinns2]

reacharound in quark creating issue with placing slabs

slabs, when edge placed against top slabs using reacharound, will be placed in bottom slab configuration, leaving a step down and making it impossible to use reacharound to create a top slab platform.

slabs, when edge placing below a top slab using reacharound, will not be placed in the bottom slab config to create a full block. but will instead be placed in the cell directly below that one as a top slab. leaving a half block gap between the two slabs.

problem seems to be a re-occurrence of a previous issue that was apparently resolved some time ago as seen here.

#1447