message: vertexcodec: Fix encoding for vertex_count = 0
  It's not clear if this is really useful, but just in case it is this
  fixes the crash when encoding an empty vertex buffer; last vertex will
  be zeroed out in this case. Decoder already supports vertex_count = 0
  without changes.
diff: @@ -755,7 +755,8 @@ size_t meshopt_encodeVertexBuffer(unsigned char* buffer, size_t buffer_size, con
  *data++ = kVertexHeader;
  - unsigned char last_vertex[256];
  + unsigned char last_vertex[256] = {};
  + if (vertex_count > 0)
  memcpy(last_vertex, vertex_data, vertex_size);
  size_t vertex_block_size = getVertexBlockSize(vertex_size);
  