dwifslpreproc: Minor fixes
dwifslpreproc: Minor fixes

- On EddyQC failure, write text file containing stdout / stderr contents in binary mode, just as is done for eddy (#2313).
- For EddyQC exports, deal with prospect of whitespace in output directory path.

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