Off-by-one problem with 2x scaling

[mark_k]

I noticed a small problem when scaling is set to 2x in H or V directions. This is with D3D output. Happens in Wine and Windows Vista (in both cases using Nvidia driver). I originally noticed it when testing NetBSD; I had vertical scaling set to 2x so the boot console text is more readable.

When output scaling is set to 2x in H and/or V directions and the emulation window is smaller than the scaled display, sometimes one row/column of pixels is missing. You may need to change the window size several times for the problem to show up.

I checked some older WinUAE versions:
2.4.1: problem not present (as far as I could tell)
2.4.2b1: I noticed the problem once but couldn't reproduce it
2.5.0b13: problem not present (as far as I could tell)
2.5.0b17: problem is present

Attached are pics taken in Windows Vista, 1x scaling and 2x scaling. Also an archive with three WBPattern presets which could help show the problem.