Fix for cannon material init
Fix for cannon material init

No contact materials are used. Each impostor has its unique material
that defines the friction and restitution.

RaananW/Babylon.js,Kesshi/Babylon.js,jbousquie/Babylon.js,sebavan/Babylon.js,abow/Babylon.js,Hersir88/Babylon.js,RaananW/Babylon.js,NicolasBuecher/Babylon.js,sebavan/Babylon.js,jbousquie/Babylon.js,Temechon/Babylon.js,NicolasBuecher/Babylon.js,RaananW/Babylon.js,Kesshi/Babylon.js,NicolasBuecher/Babylon.js,sebavan/Babylon.js,Temechon/Babylon.js,Hersir88/Babylon.js,BabylonJS/Babylon.js,Kesshi/Babylon.js,Temechon/Babylon.js,Hersir88/Babylon.js,jbousquie/Babylon.js,BabylonJS/Babylon.js,abow/Babylon.js,BabylonJS/Babylon.js,abow/Babylon.js