virtio-serial: Send out guest data to ports only if port is opened

Data should be written only when ports are open.

Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

hw/virtio-serial-bus.c

@@ -335,6 +335,11 @@ static void handle_output(VirtIODevice *vdev, VirtQueue *vq)
             goto next_buf;
         }
 
+	if (!port->host_connected) {
+            ret = 0;
+            goto next_buf;
+        }
+
         /*
          * A port may not have any handler registered for consuming the
          * data that the guest sends or it may not have a chardev associated