BUG/MEDIUM: mux-h1: Properly close H1C if an error is reported before sending data

BUG/MEDIUM: mux-h1: Properly close H1C if an error is reported before sending data

It is possible to have front H1 connections waiting for the client timeout
while they should be closed because a conneciton error was reported before
sebding an error message to the client. It is not a leak because the
connections are closed when the timeout expires but it is a waste of
ressources, especially if the client timeout is high.

When an early error message must be sent to the client, if an error was
already detected, no data are sent and the output buffer is released. At
this stage, the H1 connection is in CLOSING state and it must be
released. But because of a bug, this is not performed. The client timeout is
rearmed and the H1 connection is only closed when it expires.

To fix the issue, the condition to close a H1C must also be evaluated when
an error is detected before sending data.

It is only an issue with idle client connections, because there is no H1
stream in that case and the error message is generated by the mux itself.

This patch must be backported as far as 2.8.