Blender Git Loki

DataTransfer: Fix vertices being wrongly added to vgroup.

Previously, a vertex from destination mesh would always be added to all
transferred vgroup (with a 0.0 weight), even if none of its matching
sources in source mesh belonged to the matching source vgroups.

Now a destination vertex is only added to a given destination vgroup if
at least one of its source vertices belong to the matching source
vgroup.

Issue found and initial investigation by @pls in D11524, thanks!