Missing walls with compat renderer

[_mental_]

The compatibility renderer has a problem with particular walls. For example warp 2720 -200 -32 on Extreme Terror:

Screenshot_Doom_20160629_114335.jpg (43.51 KiB) Viewed 509 times

During the investigation I found a typo which causes this issue.

[Graf Zahl]

Thanks for these fixes. Still, you do have access to the repo and there's really no need to let me review such things so you have my explicit permission to directly commit them.

[_mental_]

OK, thanks.

[_mental_]

Sorry for bumping this topic but apparently the problems wasn't fixed completely.
Have no idea how I checked it previously but with the latest commit it looks like this:

exterror_door.jpg (62.43 KiB) Viewed 477 times

In order to fix the missing wall I came up with the fix. Graf, it's definitively requires your review.

Moreover even with this change there are some small black triangles which are not present with the modern renderer (I checked on nVidia OpenGL 4.5 Core).

exterror_triangle_1.jpg (60.07 KiB) Viewed 477 times

exterror_triangle_2.jpg (62.99 KiB) Viewed 477 times

Unlike missing parts of the door this issue reproduces with GZDoom 1.9.1 too.