Stream handler not applied correctly when mapping/flatMapping

[mpilquist]

scala> Stream.fail(new RuntimeException).onError(Stream.emit).toList
res22: List[Throwable] = List(java.lang.RuntimeException)

scala> Stream.fail(new RuntimeException).onError(Stream.emit).map(identity).toList
java.lang.RuntimeException
  ... 42 elided

Originally spotted by @fiadliel in a larger example involving concurrent.join.