MINOR: mux-h1: Set EOI on SE during demux when both side are in DONE state

MINOR: mux-h1: Set EOI on SE during demux when both side are in DONE state

For now, this case is already handled for all requests except for those
waiting for a tunnel establishment (CONNECT and protocol upgrades). It is
not an issue because only bodyless requests are supported in these cases. So
the request is always finished at the end of headers and therefore before
the response.

However, to relax conditions for full H1 protocol upgrades (H1 client and
server), this case will be necessary. Indeed, the idea is to be able to
perform protocol upgrades for requests with a payload. Today, the "Upgrade:"
header is removed before sending the request to the server. But to support
this case, this patch is required to properly finish transaction when the
server does not perform the upgrade.