fix NoneType errors

[bgruening]

Fix the following error:

barcode_fastq   barcodes.fastq.gz
read1   read1.fastq.gz
read2   None
bases   16
prefix  
suffix  
whitelist   None
func    <function run_barcode at 0x7f50f63389d0>
Traceback (most recent call last):
  File "/usr/local/bin/sinto", line 10, in <module>
    sys.exit(main())
  File "/usr/local/lib/python3.10/site-packages/sinto/arguments.py", line 555, in main
    options.func(options)
  File "/usr/local/lib/python3.10/site-packages/sinto/utils.py", line 24, in wrapper
    func(args)
  File "/usr/local/lib/python3.10/site-packages/sinto/cli.py", line 105, in run_barcode
    addbarcodes.addbarcodes(
  File "/usr/local/lib/python3.10/site-packages/sinto/addbarcodes.py", line 100, in addbarcodes
    if len(whitelist) > 0:
TypeError: object of type 'NoneType' has no len()

[timoast]

Thanks @bgruening !