Fix broken pipe handling

Fix broken pipe handling

Metze is right: If we have *any* error at the socket level, we just can
not continue.

Also, apply some defensive programming: With this async stuff someone else
might already have closed the socket.
(cherry picked from commit f140bf2e6578e45b8603d4a6c5feef9a3b735804)

Signed-off-by: Stefan Metzmacher <metze@samba.org>
(cherry picked from commit 67b51cc9e773fcbbc2b942a1de256e2c5b695008)