Change internalHandleStreamReady() to onl add to activeCpClients when…

… there hasn't been an active client for that authority rather than using the generic add method all of the time.

xds/src/main/java/io/grpc/xds/client/XdsClientImpl.java

@@ -1068,8 +1068,8 @@ public void handleStreamRestarted(ServerInfo serverInfo) {
     private void internalHandleStreamReady(
         ServerInfo serverInfo, ControlPlaneClient controlPlaneClient, String authority) {
       ControlPlaneClient activeCpClient = getActiveCpc(authority);
-      addCpcToAuthority(authority, controlPlaneClient);
       if (activeCpClient == null) {
+        activeCpClients.computeIfAbsent(authority, k -> new ArrayList<>()).add(controlPlaneClient);
         restartMatchingSubscriberTimers(authority);
         controlPlaneClient.sendDiscoveryRequests();
         return; // Since nothing was active can ignore fallback