message: Fix a crash if an instanced property has a step rate of 0
diff: @@ -225,10 +225,10 @@ void D3D11Replay::RenderMesh(uint32_t eventId, const vector<MeshFormat> &seconda
  // we source all data from the first instanced value in the instanced case, so make sure we
  // offset correctly here.
  - if(cfg.position.instanced)
  + if(cfg.position.instanced && cfg.position.instStepRate)
  offs[0] += cfg.position.vertexByteStride * (cfg.curInstance / cfg.position.instStepRate);
  - if(cfg.second.instanced)
  + if(cfg.second.instanced && cfg.second.instStepRate)
  offs[1] += cfg.second.vertexByteStride * (cfg.curInstance / cfg.second.instStepRate);
  {
  