Map Renderer|WallEdge|Client: Cluster-internal edges need no neighbor intercepts

We can skip neighbor intercepting for the sides of wall edges whose
half-edge is an internal edge of some sector cluster. This is because
such an edge only ever produces middle wall sections, which, do not
support divisions in any case (they become vissprites).

This prevents broken map geometry leading us into an infinite loop.
Fixed|Doom: Icon of Sin explosions spawn too high

Due to a fixed/floating point mix up.