[zdoom-r3190]New 3d Floors issue in software renderer

[AC3]

I found a problem related to 3D Floors, always concentrating on the latest build.

1- The mid texture of the 3d floor attached to a wall.

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This issue doesnt happen in Open GL mode.

In other ports I tested, the transfer heights aren't working by the 3d Floor code. (I doubt if that's the conflict.) But on this port the transfer height works fine.

EDIT: Here's an example WAD

[kgsws-CZ]

Fixed. This fix will not work correctly if ceiling (or floor) of real sector is sloped.
This patch also fixes another bug with fake walls of hidden 3D floors.