Blender Git Loki

Fix T52679: Hole in bake normal

In fact, any type of baking might have caused holes in mesh.

The issue was caused by zspan_scanconvert() attempting to get order of traversal
'a-priori', which might have failed if check happens at the "tip" of span where
`zspan->span1[sn1] == zspan->span2[sn1]`.

Didn't see anything bad on making it a check when iterating over scanlines and
pick minimal span based on current scanline. It's slower, but unlikely to cause
measurable difference. Quality should stay the same unless i'm missing something.

Reviewers: brecht, dfelinto

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D2837