GRAPHICS: Fix potential bug in drawThickLine2

[ccawley2011]

This was encountered during the development of PR #6374 where the loop iterator wasn't being used and each point was being plotted in the same place.

The function is only used in the SCI engine, but I'm not sure which games use it and where.

[sluicebox]

I don't think any supported SCI games use this.

The only calls to GfxPaint32::makeLineBitmap with a potential thickness > 1 are kernel functions kAddLine and kUpdateLine. I searched my script repo for all calls to these two, and there are very few. Only two games pass a thickness > 1.

One is Torin, which passes 2 on the chapter selection screen, but GfxPaint32::makeLineBitmap rounds 2 down to 1.

The other is Hoyle5, it passes a thickness of 7 in its SpeakWindow class, but the class is not used in the CD versions, and those are all we support. Maybe it's used in the floppy versions, but we will never support them because they don't contain menu resources.

[bluegr]

Thanks! I've fixed the conflict via the github UI. Squashing