Painting weights in Grease Pencil with the auto-normalize option enabled,
gave unpredictable results when vertex groups with a weight of zero
were involved.
This patch resolves the issue. Vertex weights of zero are excluded from
auto-normalization. Which is a better fit for the Grease Pencil workflow,
where weights are mostly painted from scratch since the 'parent to
armature with automatic weights' operator doesn't give good results.
Pull Request: https://projects.blender.org/blender/blender/pulls/108524
a784a65dbe