Blender Git Loki

fix [#30101] Vertex colors disappear after leaving edit mode

this commit makes vertex paint check if it needs to rebuild the modifier stack when painting.
- when painting with no modifiers, do partial updates from polys to tessfaces while painting, skip re-tesselation.
- when painting onto a modified mesh, dont bother adjusting tessface colors - since the modifier stack will do this anyway.

both cases should be faster then before.