Contrast with:
```scala
      Thread.currentThread match {
        case fjw: ForkJoinWorkerThread if fjw.getPool eq fj => fjt.fork()
        case _                                              => fj execute fjt
      }
```
(from https://github.com/scala/scala/blob/master/src/library/scala/concurrent/impl/ExecutionContextImpl.scala#L105)

Why does that code need to check for `fjw.getPool eq fj`? Is that check missing here?