3D vision allows looking through 1 tile opaque obstacles (the "Pillar Bug")

[Coolthulhu]

Describe the bug

When 3D vision mode is on, you can see through 1 tile wide opaque obstacles.

The bug also affects other types of obstacles, such as diagonal vehicle vision blockers, effectively making vehicles semi-transparent when turned diagonally. This only affects shadowcasting, not monster-to-monster vision. Monster-to-player vision uses player's shadowcasting results and so it is also affected.

Steps To Reproduce

1. Remove clairvoyance, turn on 3D vision, have enough sight range to see at least 10 tiles
2. Spawn a 1 tile pillar directly orthogonal to player
3. Look through the pillar as if it wasn't there

Expected behavior

The pillar should block vision in a cone behind it.

Screenshots

Versions and configuration

Affects all systems.

Additional context

No response