prepare_write_connect() prepares a connect message, then sets
WRITE_PENDING on the connection. Then *after* this, it calls
prepare_connect_authorizer(), which updates the content of the
connection buffer already queued for sending. It's also possible it
will result in prepare_write_connect() returning -EAGAIN despite the
WRITE_PENDING big getting set.
Fix this by preparing the connect authorizer first, setting the
WRITE_PENDING bit only after that is done.