mailpipe: respond with the fleshed out message, not the original.

mailpipe: respond with the fleshed out message, not the original.

We've just added an author, targets, subject, etc.  None of that
matters if you send the original version.

Also print check that the subject is not None before we remove any
subject fields.  This shouldn't matter (del-ing a None subject should
be a no-op), but it seems safer to print the offending message before
messing with it.