can't use conc_exec.map in slicing.py

[wpNZC]

can't use conc_exec.map in slicing.py,and the _export_single_slice is invalid,now I have to use
" for i in range(len(sliced_image_result.images)):
_export_single_slice(sliced_image_result.images[i],output_dir,sliced_image_result.filenames[i])"to instead