Error out when tls-channel option is used without TLS

It's currently possible to setup spice channels using TLS when
no TLS port has been specified (ie TLS is disabled). This cannot
work, so better to error out in such a situation.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

ui/spice-core.c

@@ -511,6 +511,12 @@ static int add_channel(const char *name, const char *value, void *opaque)
     int rc;
 
     if (strcmp(name, "tls-channel") == 0) {
+        int *tls_port = opaque;
+        if (!*tls_port) {
+            error_report("spice: tried to setup tls-channel"
+                         " without specifying a TLS port");
+            exit(1);
+        }
         security = SPICE_CHANNEL_SECURITY_SSL;
     }
     if (strcmp(name, "plaintext-channel") == 0) {
@@ -680,7 +686,7 @@ void qemu_spice_init(void)
     spice_server_set_playback_compression
         (spice_server, qemu_opt_get_bool(opts, "playback-compression", 1));
 
-    qemu_opt_foreach(opts, add_channel, NULL, 0);
+    qemu_opt_foreach(opts, add_channel, &tls_port, 0);
 
     if (0 != spice_server_init(spice_server, &core_interface)) {
         error_report("failed to initialize spice server");