rpc: avoid memory leak on error

Detected by Coverity.  The leak is on an error path, but I'm not
sure whether that path is likely to be triggered in practice.

* src/rpc/virnetserverservice.c (virNetServerServiceAccept): Plug leak.

src/rpc/virnetserverservice.c

@@ -82,7 +82,12 @@ cleanup:
     return;
 
 error:
-    virNetSocketFree(clientsock);
+    if (client) {
+        virNetServerClientClose(client);
+        virNetServerClientFree(client);
+    } else {
+        virNetSocketFree(clientsock);
+    }
 }