Python: Restore fix to ProgressBar line wrapping
Python: Restore fix to ProgressBar line wrapping

Fix was applied in 65e41c12 / #1837, but appears to have been lost in merge e0223ed9 for #1605.

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