screen: fix exiting on client disconnect with new libspice-server

the way we detected a client_disconnect does not work anymore with
spice-server >= 0.14.3, but there is a convienient function
that exits the spice-server on client disconnect

there is a slight behaviour change that should not make a big difference:

previously, if a user used the same '.vv' file twice, the first client
got disconnected and the second would connect

now, because the server closes on disconnect, the second client is
not be able to connect anymore

using our ui though, every click on 'shell>spice' generates a new '.vv'
file that works though (and for container shells we use dtach to mux)

i could not (in reasonable time) find out why the first client
disconnects at all, and also could not find another way to detect a
client disconnect that is similar to our previous method

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

src/screen.c

@@ -789,6 +789,8 @@ spice_screen_new(
         }
     }
 
+    spice_server_set_exit_on_disconnect(server, 1);
+
     int res = spice_server_init(server, core);
     if (res != 0) {
         g_error("spice_server_init failed, res = %d\n", res);