tr2/objects/door: reset sector tilt on closed doors

The legacy approach would reset the FD index to 0, but this was missed
in the FD refactor in #1896. The result was NO_HEIGHT would be
manipulated by the tilt values and hence could produce invisible
geometry.

src/tr2/game/objects/general/door.c

@@ -67,6 +67,8 @@ void __cdecl Door_Shut(DOORPOS_DATA *const d)
     sector->box = NO_BOX;
     sector->ceiling.height = NO_HEIGHT;
     sector->floor.height = NO_HEIGHT;
+    sector->floor.tilt = 0;
+    sector->ceiling.tilt = 0;
     sector->portal_room.sky = NO_ROOM_NEG;
     sector->portal_room.pit = NO_ROOM_NEG;
     sector->portal_room.wall = NO_ROOM;