Doors vanished by pit bloats or descent still block line of sight

[withinwheels]

If the door tile is no longer displayed then it seems only fair to be able to see past them. Or let things on the other side see you..

[nstoddard]

Intuitively it seems like the door tiles should remain visible; presumably, they're attached to an adjacent wall by hinges, and unless something happens to that wall, the door would remain in place.