Multipart meshes (OrganelleMeshWithChildren) don't display dissolve animation as chunks correctly

[hhyyrylainen]

When displaying the fade animation on organelle made up of multiple meshes it displays fine in a microbe, but when in a dropped chunk the fade animation is only played on the main model. This would be pretty nice to fix. Seems likely the problem is missing handling for OrganelleMeshWithChildren in getting the materials to play animations on for chunks.