Update ChFilters.cpp
Update ChFilters.cpp

Small fixes to avoid possible problems:
- maxval could give wrong results when all vector elements are negative.
- wrong data type could lead to illegal element references in large data sets

dariomangoni/chrono,dariomangoni/chrono,rserban/chrono,projectchrono/chrono,Milad-Rakhsha/chrono,projectchrono/chrono,dariomangoni/chrono,dariomangoni/chrono,Milad-Rakhsha/chrono,Milad-Rakhsha/chrono,dariomangoni/chrono,projectchrono/chrono,rserban/chrono,projectchrono/chrono,Milad-Rakhsha/chrono,projectchrono/chrono,Milad-Rakhsha/chrono,rserban/chrono,rserban/chrono,rserban/chrono,projectchrono/chrono,rserban/chrono,rserban/chrono,dariomangoni/chrono,Milad-Rakhsha/chrono