xen_console: ignore console disconnect events from console/0

The first console has a different location compared to other PV devices
(console, rather than device/console/0) and doesn't obey the xenstore
state protocol. We already special case the first console in con_init
and con_initialise, we should also do it in con_disconnect.
Signed-off-by: NStefano Stabellini <stefano.stabellini@eu.citrix.com>

hw/xen_console.c

@@ -248,6 +248,9 @@ static void con_disconnect(struct XenDevice *xendev)
 {
     struct XenConsole *con = container_of(xendev, struct XenConsole, xendev);
 
+    if (!xendev->dev) {
+        return;
+    }
     if (con->chr)
         qemu_chr_add_handlers(con->chr, NULL, NULL, NULL, NULL);
     xen_be_unbind_evtchn(&con->xendev);