www: gzip_filter: gracefully handle socket ->write failures
Socket ->write failures are expected and common for TCP traffic,
especially if it's facing unreliable remote connections. So
just bail out silently if our {gz} field was already clobbered
during the small bit of recursion we hit on ->write failures
from async responses.
This ought to fix some GzipFilter::zflush errors (via $forward
->close from PublicInbox::HTTP) I've been noticing on
deployments running -netd. I'm still unsure as to why I hadn't
seen them before, but it might've only been ignorance on my
part...
Link: https://public-inbox.org/meta/20220802065436.GA13935@dcvr/