chat-store: fix errant 'this'
chat-store: fix errant 'this'

6c938e1 resolved a merge conflict, but retained a reference to 'this'
from the wrong parent.

jfranklin9000/urbit,ngzax/urbit,ngzax/urbit,jfranklin9000/urbit,urbit/urbit,jfranklin9000/urbit,urbit/urbit,jfranklin9000/urbit,jfranklin9000/urbit,urbit/urbit,urbit/urbit,ngzax/urbit,ngzax/urbit,jfranklin9000/urbit,ngzax/urbit,ngzax/urbit,urbit/urbit,urbit/urbit,ngzax/urbit,jfranklin9000/urbit,urbit/urbit