Call destructor if thread was ever constructed

src/core/tsi/alts_transport_security.cc

@@ -55,6 +55,7 @@ void grpc_tsi_alts_shutdown() {
     grpc_completion_queue_destroy(g_alts_resource.cq);
     grpc_channel_destroy(g_alts_resource.channel);
     g_alts_resource.thread.Join();
+    g_alts_resource.thread.~Thread();
   }
   gpr_cv_destroy(&g_alts_resource.cv);
   gpr_mu_destroy(&g_alts_resource.mu);