Drain pending requests on language server termination (#4852)

This prevents a freeze while shutting down when using `efm-langserver`.
`efm-langserver` exits immediately after seeing a shutdown request,
without responding to the request. We block awaiting the reply to the
shutdown request which will never come, so we time out.

This change responds to any pending requests with `Err` saying that the
stream has been closed.

0 files changed, 0 insertions, 0 deletions