src: document required else block at src/node_platform.cc

PR-URL: #34688
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>

src/node_platform.cc

@@ -409,6 +409,9 @@ void PerIsolatePlatformData::RunForegroundTask(std::unique_ptr<Task> task) {
                                    InternalCallbackScope::kNoFlags);
     task->Run();
   } else {
+    // The task is moved out of InternalCallbackScope if env is not available.
+    // This is a required else block, and should not be removed.
+    // See comment: https://github.com/nodejs/node/pull/34688#pullrequestreview-463867489
     task->Run();
   }
 }