Fix compiler warnings for scene viewer input C++ header from previous commit. Also change to pass reference for process input method. Issue 3662.
Fix compiler warnings for scene viewer input C++ header from previous commit. Also change to pass reference for process input method. Issue 3662.

OpenCMISS/zinc,OpenCMISS/zinc,hsorby/zinc,OpenCMISS/zinc,hsorby/zinc,hsorby/zinc,OpenCMISS/zinc,hsorby/zinc