client rpc: Process pending data on error

client rpc: Process pending data on error

Even though we hit an error in client's IO loop, we still want to
process any pending data. So instead of reporting the error right away,
we can finish the current iteration and report the error once we're done
with it. Note that the error is stored in client->error by
virNetClientMarkClose so we don't need to worry about it being reset or
rewritten by any API we call in the meantime.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>