mrthreshold: Suppress prgressbars if writing to cout
mrthreshold: Suppress prgressbars if writing to cout

If no output image path is specified to mrthreshold, and therefore it will be writing the determined threshold values to the standard output stream, then progress bars should not be displayed on the terminal, as these can overwrite the values written to standard output.

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