ubuntu 20.04 bug fixed

[valenbase]

Thanks for your work.

I used the code under ubuntu 20.04, which meets two bugs,

1. scans crash
   int FreeSeg(float *fPoints,int *pLabel,int pointNum)
   adds return value;
   int PCSeg::DoSeg(int *pLabel1, float* fPoints1, int pointNum)
   adds return value;
2. pose estimation crash
   double ComputeError(const Eigen::Matrix4d& pose)
   adds return error;