Raise exception when CosmeticChangesToolkit gets no namespace
Raise exception when CosmeticChangesToolkit gets no namespace

self.talkpage = self.namespace >= 0 and self.namespace % 2 == 1 raises
an exception anyway, so let's raise a more descriptive one.

Change-Id: Id22053956bcf7b7454c722fdda4043d116d51d2a

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