Fix: Don't overwrite `post-status` if set
I was finding that Micropublish, oddly, kept marking my Week Notes as
draft
even when they were published, so then by changing them to
published
would lead to the published
property be updated, which
wasn't expected.
It turns out we were overwriting whatever was set, always showing in
q=source
as the post being a draft, even if it wasn't.