chat: handle suffixes and readers when adding username to TLF
chat: handle suffixes and readers when adding username to TLF

Otherwise a valid TLF name like "a,b (conflicted copy 2019-02-14 #1)"
becomes "a,b (conflicted copy 2019-02-14 #1),a" and everything breaks.

keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client