pagegenerators.py: -linter options fails
pagegenerators.py: -linter options fails

Fix parsing of argument in handleArg()
-linter should select all categories instead gives error.

Bug: T187945
Change-Id: I462ef0c7f32a1a519f9d7f394372aaa6e93d3bf4

wikimedia/pywikibot-core,wikimedia/pywikibot-core,PersianWikipedia/pywikibot-core