msdwi2fod: minor change to allow compilation after switch to C++11 threading API
msdwi2fod: minor change to allow compilation after switch to C++11 threading API

MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3