remove 'else' code, release lock by destructor

src/cpp/server/server.cc

@@ -179,12 +179,12 @@ Server::Server(ThreadPoolInterface* thread_pool, bool thread_pool_owned)
       thread_pool_owned_(thread_pool_owned) {}
 
 Server::~Server() {
+  {
     std::unique_lock<std::mutex> lock(mu_);
     if (started_ && !shutdown_) {
       lock.unlock();
       Shutdown();
-  } else {
+    }
-    lock.unlock();
   }
   grpc_server_destroy(server_);
   if (thread_pool_owned_) {