[g4.8pre] Some sector shapes break Hexen stairs

[treacherousfiend]

It seems there's an issue with Hexen style stairs where certain sector shapes will break them, causing only the first 2 steps to be lowered.
I noticed this issue in MAP04 of GERMS V1F (viewtopic.php?f=42&t=65498), and was frustrated enough by it that I decided to look into it.
I've only been able to reproduce this bug with sectors shaped like a trapezoid, with the smallest step being the first one.

A test map I made can be found attached with 3 demonstration stairs.
The stairs on the left have a pretty strong angle (157 degrees), But still work for some reason
The middle stairs have a more slight angle (164 degrees), But are affected by this bug
The stairs on the right are directly copy-pasted from the broken stairs I found in GERMS.

I also used my extremely limited git knowledge to try bisecting the issue and narrowed the problem commit down to commit 63fa01205f9b111c8e6b27b54fe736f834b6b807 (
- fixed potential infinite loop in Hexen-style stair builder. Jan 6
But I unfortunately am not sure what the actual root of the problem is.
Considering the fact that the first 2 stairs work fine, it seems like it might be an issue with detecting the next sector with special 26 (Hexen stairs swap between specials 26 and 27 with every sector)

[Graf Zahl]

fixed. Actually, the shape of the sector does not matter - the bug happened when the lowest numbered line to a sector with the alternative stair special is the initial sector where the stair building started. This was not properly flagged as having been processed.

[treacherousfiend]

interesting, since I had a working stair which became not working through making it an odd shape, correlation not causation I guess. thanks for the quick fix!