Fix a bug for convert_recursive

To fix following error:

$ xlsx2csv -a . csv
Traceback (most recent call last):
  File "/usr/local/bin/xlsx2csv", line 546, in <module>
    convert_recursive(options.infile, sheetid, kwargs)
  File "/usr/local/bin/xlsx2csv", line 474, in convert_recursive
    convert_recursive(fullpath, kwargs)
TypeError: convert_recursive() takes exactly 3 arguments (2 given)