Mail: handling of read buffer filled with commands. If the whole read buffer was filled with commands during authentication, exactly matching the buffer boundary, this did not cause the "client sent too long command" error, but might result in read events being disabled for the connection, notably with level-triggered event methods, leading to a connection hang. Fix is to ensure that s->blocked is set in case of c->read->ready, so command reading is resumed after sending responses to previous commands.