Fix the initial pressure issue of the SPH terrain for the VIPER rover demo
Fix the initial pressure issue of the SPH terrain for the VIPER rover demo

dariomangoni/chrono,rserban/chrono,projectchrono/chrono,rserban/chrono,rserban/chrono,dariomangoni/chrono,projectchrono/chrono,dariomangoni/chrono,dariomangoni/chrono,rserban/chrono,rserban/chrono,projectchrono/chrono,projectchrono/chrono,projectchrono/chrono,dariomangoni/chrono,rserban/chrono,dariomangoni/chrono,projectchrono/chrono,rserban/chrono