openuriportal: Detect if the interface isn't there

Check the portal version number before trying to use
it. Most importantly, this will detect the case where
the interface isn't supported at all, since the proxy
will report a version of 0 in that case.

Fixes: #5733

gtk/gtkopenuriportal.c

@@ -67,6 +67,12 @@ init_openuri_portal (void)
               g_error_free (error);
             }
 
+          if (gtk_xdp_open_uri_get_version (openuri) < 3)
+            {
+              g_warning ("Not a supported version of the OpenURI portal: %u", gtk_xdp_open_uri_get_version (openuri));
+              g_clear_object (&openuri);
+            }
+
           g_object_unref (connection);
         }
       else