Josh realized that with new Chrome, because we don't support the type of
compression extension yet we returned a null extension header.
This patch fixes that by deferring issuing the extension header until we
find we have something to say.
tested OK on google-chrome 19.0.1081.2-129295
Reported-by: Josh Roberson <josh@asteriasgi.com>
Signed-off-by: Andy Green <andy.green@linaro.org>