Fix T98385: Color attributes not working with GPU subdivision

Contrary to coarse extraction, GPU extraction uses the same buffer for
the coarse data, only the final GPU buffer needs to be offset.

source/blender/draw/intern/mesh_extractors/extract_mesh_vbo_vcol.cc

@@ -271,8 +271,6 @@ static void extract_vcol_init_subdiv(const DRWSubdivCache *subdiv_cache,
 
   blender::Vector<VColRef> refs = get_vcol_refs(cd_vdata, cd_ldata, vcol_layers);
 
-  gpuMeshVcol *vcol = mesh_vcol;
-
   /* Index of the vertex color layer in the compact buffer. Used vertex color layers are stored in
    * a single buffer. */
   int pack_layer_index = 0;
@@ -287,10 +285,10 @@ static void extract_vcol_init_subdiv(const DRWSubdivCache *subdiv_cache,
 
     if (layer_i == -1) {
       printf("%s: missing color layer %s\n", __func__, ref.layer->name);
-      vcol += coarse_mesh->totloop;
       continue;
     }
 
+    gpuMeshVcol *vcol = mesh_vcol;
     MLoopCol *mcol = nullptr;
     MPropCol *pcol = nullptr;