[bugfix] Don't use mixed bytestring and unicode for filename
[bugfix] Don't use mixed bytestring and unicode for filename

Bug: T163349
Change-Id: If030c2db5e41a3786ec7c87fada1906cc03599a6

wikimedia/pywikibot-core,npdoty/pywikibot,npdoty/pywikibot,magul/pywikibot-core,hasteur/g13bot_tools_new,hasteur/g13bot_tools_new,happy5214/pywikibot-core,happy5214/pywikibot-core,hasteur/g13bot_tools_new,PersianWikipedia/pywikibot-core,magul/pywikibot-core,wikimedia/pywikibot-core