message: Apply vertex offset to indices
  Fixes rendering for other models like sponza
  Refs
diff: @@ -313,6 +313,8 @@ private:
  bool hasColor = aMesh->HasVertexColors(0);
  bool hasNormals = aMesh->HasNormals();
  + const uint32_t vertexOffset = static_cast<uint32_t>(vertices.size());
  +
  for (uint32_t v = 0; v < aMesh->mNumVertices; v++)
  {
  Vertex vertex;
  @@ -330,7 +332,7 @@ private:
  {
  for (uint32_t j = 0; j < 3; j++)
  {
  - indices.push_back(aMesh->mFaces[f].mIndices[j]);
  + indices.push_back(vertexOffset + aMesh->mFaces[f].mIndices[j]);
  }
  }
  