message: videoio(dshow): add NULL ptr check
diff: @@ -2731,6 +2731,7 @@ int videoInput::start(int deviceID, videoDevice *VD){
  }
  VIDEOINFOHEADER *pVih = reinterpret_cast<VIDEOINFOHEADER*>(VD->pAmMediaType->pbFormat);
  + CV_Assert(pVih);
  int currentWidth = HEADER(pVih)->biWidth;
  int currentHeight = HEADER(pVih)->biHeight;
  